18th International Workshop on Low Temperature Detectors (LTD-18)

Europe/Rome
Auditorium G. Testori (Milano)

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
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Description
The International Workshop on Low Temperature Detectors (LTD) is the biennial meeting where experts from all over the world meet to share and discuss latest results and new ideas in the field of cryogenic detectors and their applications.
Low temperature detectors with their outstanding characteristics enable unconventional methods for high precision measurements. Their unique and promising features led to rapid technical developments in the last years, which made these detectors very attractive in a wide variety of fields from fundamental research to applied sciences. Astronomy and astrophysics, dark matter, nuclear and particle physics, X-ray material analysis, thin films, semiconductor and superconductor applications, ion spectroscopy and biomolecule mass spectrometry are now major research areas. Technologies commonly exploited by LTD-18 scientists include cryogenics, cryo-electronics, thin-film deposition, superconductivity, nano- and micro- fabrication, signal read-out multiplexing, data acquisition and analysis.
This 18th workshop will be co-hosted by Universita' di Milano-Bicocca and Istituto Nazionale di Fisica Nucleare and will take place from July 22 to July 26 of 2019 in Milano, at Palazzo Lombardia (headquarters of the Lombardia region) in the Directional Center of Milano. More than 300 physicists and engineers are expected from over 50 top-level Universities and Research Institutes worldwide.
Official website for information and registration at https://www.ltd18.unimib.it/

Support email
• Sunday, July 21
• LTD-18 registration: Welcome buffet Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Monday, July 22
• LTD-18 registration: Registration Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Openings Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Tutorials Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• 1
Low Temperature Detector Development and Physics
Speaker: Dr Caroline Kilbourne (NASA-GSFC)
• 2
Low Temperature Detector Applications
Speaker: Andrea Giuliani (CSNSM Orsay)
• 10:10 AM
Coffee break Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Orals LM 001: MICRO A Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector Development and Physics

Convener: Dr Simon, R. Bandler (NASA-GSFC)
• 3
Transition Edge Sensors for HOLMES

HOLMES is an experiment with the goal of performing a direct measurement of the neutrino mass from the electron capture spectrum of 163Ho. In order to reach its goal sensitivity of 2 eV it is necessary to gather as many as 10e13 events in the three years projected live time of the experiment. To do so, HOLMES will deploy an array of 1000 low temperature calorimeters composed by a Transition Edge Sensor (TES) thermometer coupled to a gold absorber, where 163Ho will be embedded, via a custom ion implanter. With a target activity of 300 Bq for each absorber, pile-up will be the main limiting factor in the sensitivity for the neutrino mass.
In order to keep the pile-up fraction at 1e-4 it is crucial to have signals with an exponential rising edge of ~10 us sampled at a proper rate (500 kHz) so that pile-up resolving algorithms may be applied. Besides, an energy resolution of the order of few eV is needed not to spoil the neutrino mass measurement.

In this contribution I will describe the detectors used in HOLMES, their performance and the RF-SQUID based multiplexed readout system which will allow us to simultaneously operate 1000 detectors at 100 mK and collect the necessary data to reach the 2 eV target sensitivity of the neutrino mass.

Speaker: Andrei Puiu (MIB)
• 4
TES pixel optimization for the ATHENA X-IFU instrument

The Advanced Telescope for High ENergy Astrophysics (ATHENA) will include the X-ray Integral Field Unit instrument (X-IFU). This instrument is baselined with an array of 3,168 transition-edge sensor (TES) pixels made with Mo/Au bilayers that will be AC biased and Frequency-Division Mutliplexed (FDM). Over the last few years, there has been intense effort at NASA/GSFC and SRON to better understand and optimize the pixel design to meet the requirements of X-IFU. This has included investigation of the effect of TES design on transition shape and uniformity, noise, eddy-current losses, AC Josephson effects, and spectral resolution over a broad range of incident energy. Through this understanding we have been able to achieve ground-breaking performance under AC bias. In this presentation, we will discuss the important physical effects in the TES, and describe how they are driving the choice of TES parameters (size, aspect ratio, thermal conductance, resistance, heat capacity etc.) that are being considered for X-IFU. We will also discuss the latest measurements of NASA TES devices and how they are further improving our understanding of the relevant physics in the TES. This will include our advances in modeling the TES as multiple thermal bodies, and how the design of X-ray absorber attachments may influence TES performance.

Speaker: Dr Nicholas, A. Wakeham (NASA-GSFC / UMBC)
• 5
Characterization of high aspect ratio TiAu TES X-ray microcalorimeters array using the X-IFU Frequency Domain Multiplexing readout

At SRON Netherlands Institute for Space Research, we are developing X-ray microcalorimeters as backup option for the baseline detectors in the X-IFU instrument on board of the ATHENA space mission led by ESA and to be launched in the early 2030s.
New, mixed 5X5 TiAu Transition Edge Sensor (TES) arrays where TESs have different high aspect ratios and high resistance have been fabricated to meet the requirement of the X-IFU instruments. Such arrays can also be used to optimize the performances of the Frequency Domain Multiplexing (FDM) readout and eventually can lead to large detector arrays.
In this work we present the results obtained on tens of devices with an aspect ratio ranging from 1-to-1 up to 1-to-5 measured in the single pixel mode, with the FDM readout developed at SRON/VTT. We observed an nominal energy resolution of about 2.5 eV at 5.9 keV and at bias frequencies from 1 to 5 MHz. The measurements have been done in the high inductance limit regime, implying that we are still far from their intrinsic energy resolutions. Thermal and electrical parameters have been compared by means of AC complex impedance and noise spectra measurements to have a clear picture of the performances of these arrays.
These detectors are proving to be the best TES microcalorimeters ever reported in Europe, being able to accomplish not only the specifications of the X-IFU instrument, but also those ones for other future challenging X-ray space missions, fundamental physics experiments, plasma characterization and material analysis.
We are now ready to test the uniform kilo pixels array in combination with the FDM readout in multi pixels mode.

Acknowledgment

This work is partly funded by European Space Agency (ESA) under ESA CTP contract ITT AO/1-7947/14/NL/BW, and is partly by the European Union’s Horizon 2020 Programme under the AHEAD project with grant agreement number 654215.

Speaker: Dr Emanuele Taralli (SRON)
• Orals LM 001: BOLO 1 Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector Development and Physics

Convener: Prof. Sunil Golwala (California Institute of Technology)
• 6
Ultrasensitive Microwave Bolometer

Intense development of nanobolometers has taken place for well more than a decade with the aim to reach noise equivalent power NEP = 10e-20 W/rtHz. Furthermore, observation of single photons at increasingly long wavelengths is a long-standing effort. We present a microwave nanobolometer based on superconductor/normal-metal/superconductor Josephson junctions. Using positive electrothermal feedback, we show that we can achieve a single-shot detection ?fidelity of 0.56 for 1.1-zJ pulses of 8.4-GHz photons [1]. This is more than an order of magnitude improvement over the previous thermal detectors. Furthermore, we observe that we can reach NEP = 2*10e-20 W/rtHz with our detector in the linear bolometric mode [2]. The measured frequency dependence of the NEP suggest that this bolometer is capable of detecting single 0.3-zJ photons. These results were achieved by integrating the bolometer with a quantum-limited Josephson parameteric apmli?er and further improvements are expected for example using two-dimensional materials.

[1] J. Govenius, R. E. Lake, K. Y. Tan, and M. Möttönen, Phys. Rev. Lett. 117, 030802 (2016).

[2] R. Kokkoniemi et al., arXiv:1806.09397 (2018).

Speaker: Dr Mikko Möttönen (Aalto University)
• 7
A dual polarization, background limited Kinetic Inductance Detector operating between 1.4 and 2.8 THz

Future space-based observatories for the far infrared and sub-mm wave radiation, such as SPICA and the OST telescope, will need ultra-sensitive background limited detectors at frequencies above 1THz. We develop a KID that combines photon noise limited performance, high optical efficiency, broad band and dual polarization radiation coupling operating between 1.4 and 2.8THz, with a NEP below 3x10$^{-19}$W/Hz$^{1/2}$, and good agreement between the measured and expected optical efficiency. The fractional power ratio between the powers received by the dual polarized detector and by the single polarized counterpart is a factor 2.

The detector consists of a hybrid NbTiN/Al Kinetic Inductance Detector, fabricated on a Si substrate. Radiation coupling is achieved using a leaky lens antenna fabricated on a suspended SiN membrane. The radiation is coupled to the leaky lens antenna using a Si lens placed on top of it at a distance of 6μm. The absorbing section of the KID is fabricated entirely from Al, and integrated with the antenna to absorb power from both polarizations directly in the KID. The device shows photon noise limited performance with a NEP below 3x10$^{-19}$W/Hz$^{1/2}$ around 1.55THz with the expected optical efficiency. The dual polarized device receives twice as much power from an incoherent source than the single polarized one. Additionally, we measure the antenna beam pattern at the same frequency band and find a good match between the measured and simulated beams in reception. Standard transmission simulations are not fully correct due of the intrinsic multi-moded nature of the antenna. To verify the frequency coverage, we measure the frequency response using a Michelson interferometer to find broad band coupling in matching our simulations.

The presented design is upgradable to frequencies up to 10THz using e-beam lithography. These results indicate that broad band, dual polarization radiation coupling above 1THz is feasible using antenna coupled KIDs.

Speaker: Dr Juan Bueno (SRON)
• 8

After more than 15 years of development, the technical maturity of MKIDs has greatly improved. Array level demonstrations of imagers and spectrometers now exist, measuring a wide coverage of frequencies, and with multiple optical coupling schemes. However, several different technical challenges must be overcome before MKIDs reach the point where they become a general solution for the full suite of astronomical and instrumental applications. First, MKIDs have not consistently shown background limited sensitivity, especially at the low frequencies (< 1 Hz) essential to bolometric observations. Also, modern bolometric cameras require use of advanced focal planes in which the detectors are comprised of integrated circuits performing multiple functions such as optical coupling, diplexing, and on-chip filtering of multiple frequency bands within 1 spatial pixel.
Our efforts at NIST have been to both extend the successful direct-absorber style polarimeters pioneered for use in the balloon-borne instrument BLAST and in production for TolTEC, as well as integrate MKIDs into the proven mm-wave circuitry of NIST’s well-established OMT-coupled TES bolometer arrays that have been delivered to many collaborations. We have extended the direct-absorbing MKID technology to longer wavelengths and lower photon loadings by creating hybrid MKIDs combining the low capacitive loss of the TiN-Si interface with the high sensitivity and lower sheet resistance of thin Al inductors. We also prevent the well-known aging of the Al through the deposition of a thin passivation layer without compromising their performance. These sensors show photon limited performance well below 1 Hz. Furthermore, we have also integrated Al-based inductors and amorphous-Si based parallel-plate capacitors into an OMT-coupled circuit and have initial results of photon-noise limited performance.

Speaker: Michael Vissers (NIST-Boulder)
• 9
Compact spectroscopy imaging detectors for astrophysical applications

In this talk, I will present how we combine spectroscopy and imaging capabilities inside one compact device for submillimeter observations. This system is an interferometric system that has been designed to fulfill the spectroscopic requirements of a space mission. The idea is to bring a Fabry-Pérot spectrometer very close to the detector (silicon bolometers) such that they form a coupled, resonant system with enhanced detection efficiency. For this purpose, we introduce a new type of Fabry Pérot for submillimeter spectroscopy: instead of having metal mesh mirrors, we use an assembly of thin silicon sheets. Theoretical simulations have shown that the use of dielectrics instead of metals suppresses the ohmic losses thus leading to increasing the absolute efficiency of the spectrometer. In order to reach a high finesse similar to what we have in the case of interferometers made with metallic grids, we choose to assemble several silicon sheets to form one mirror as defined by the Bragg mirror theory. Moreover, we have found that the coupling of the spectrometer with the detector is close to perfect: the absorption of the whole assembly has almost 100% efficiency for wavelengths corresponding to the size of the resonant cavity of the Fabry Pérot. This system may lead to a real improvement and can reduce the observations time by a factor of 2, which is not negligible at all. In the second part of the talk, I will describe how we have built the mirrors and what optical tests we have performed to conclude that the silicon sheets are perfectly compatible with the finesse of our spectrometer. Finally, I will present the last measurements that we did with the silicon spectrometer at cold temperature (4K).

Speaker: Sophie Bounissou (CEA Saclay)
• 10
Potential methods for stray-light suppression in antenna-coupled LEKIDs

Arrays of lumped-element kinetic inductance detectors (LEKIDs) optically coupled through an antenna and transmission-line structure are a promising candidate for future cosmic microwave background (CMB) experiments. Using the separated architecture of a LEKID enables optical coupling to be realised, without the detector becoming susceptible to two-level system noise created by the amorphous-dielectric requirements of a simple microstrip feedline structure. Through initial investigations of small prototype arrays, we have shown this compact device architecture can produce intrinsic quality factors > 10$^5$, allowing for MUX ratios to exceed 10$^3$. Moreover, we have demonstrated that these devices are limited by generation-recombination or photon noise down to low modulation frequencies proving the devices are not susceptible to the fabrication requirements of any antenna feed or filtering network the device is coupled to. However, this optical configuration is highly susceptible to a reduction in sensitivity due to stray light. Here we discuss our investigation into a suitable method of stray-light suppression based on the addition of an absorbing layer compatible with our device design and present the current performance of our prototype devices.

Speaker: Amber Hornsby (Cardiff University)
• 1:10 PM
Lunch break Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Orals LM 001: MICRO KID Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector Development and Physics

Convener: Dr Gerhard Ulbricht (Dublin Institute for Advanced Studies)
• 11
Twenty Years of Microwave Kinetic Inductance Detectors: A Technical Review

Microwave Kinetic Inductance Detectors (MKIDs) were invented in 1999 at
Caltech and JPL with the promise of both high detector sensitivity and
an easy solution to scale into large arrays. Over 20 years of
significant development, MKIDs have fulfilled this promise with their
sensitivity approaching the fundamental limit and the pixel count
reaching 10^5. The technical maturity of MKIDs have brought them broad
applications in astronomical instruments from mm-wave, IR/visible to
X-ray for ground-based, sub-orbital and space missions, as well as
non-astronomical applications such as dark matter search and quantum
information science. In this talk, I will review the technical progress
in the understanding of device physics, the techniques invented for
improving the sensitivity, the implementation of various optical
coupling schemes, the study of materials, and the development of
fabrication process for large arrays, made over the past 20 years.

Speaker: Dr Jiansong Gao (NIST)
• 12
Results from X-Ray microcalorimeter arrays based on Thermal MKIDs (TKIDs)

I describe the design, principle of operation and results from our X-ray TKID prototype arrays. These superconducting pair-breaking detectors exploit the ease with which MKIDs can be frequency-domain multiplexed to create large arrays of X-ray microcalorimeters with absorbers that can be close-packed and tiled. Arrays of 20,000+ TKIDs are potentially achievable using frequency domain multiplexing electronics that are similar to those already used to read out 20,000+ pixel MKIDs optical arrays. Sensitivity is controlled by placing absorbers with tuned heat capacity on thermally isolated membranes and by use of low T$_c$ superconductors. Noise, from two-level systems and the readout, is minimized by control of the MKID geometry and use of very low noise amplifiers. Quantum efficiency is tuned by selection of X-ray absorber materials and thicknesses, just as for TES X-ray microcalorimeters. While the energy resolution of past devices is 75 eV at 5.9 keV, we report on progress to achieve 10 eV resolution in forthcoming design iterations. Results include the quiescent performance of individual TKID resonators and initial X-ray pulse data.

Speaker: Miguel Daal (UCSB)
• 13
Energy resolution of aluminium photon-counting MKID detectors at visible and near-infrared wavelengths

To answer the question whether there is life on exoplanets a new generation of instruments is required that will take spectra of these planets. Future instruments for visible/near-IR wavelengths therefore require noiseless, photon counting detectors, with energy resolution.
Microwave Kinetic Inductance Detectors (MKIDs) are photon-counting superconducting detectors which provide energy resolution in each pixel. The resolving power (R=E/dE) of MKIDs is theoretically limited to R~100 by Fano statistics, depending on the material. Current detectors reach R~10, thus we need to better understand the physics and improve the detector limits.
We present an energy resolution study with aluminium MKIDs, which we have previously shown to understand very well and which are the most sensitive terahertz MKIDs to date. We deliberately study a well-understood material first, before moving to higher resistivity materials, which are favourable from a photon-absorption standpoint. We have measured the resolving power of Al MKIDs, which from their THz sensitivity promise R~60 at 400 nm. We operate the MKIDs at 120 mK and illuminate them with 4 lasers between 402-1550 nm. Firstly, we find that our BK7 and fused silica windows are open to low frequency stray light (< 1 THz), which limits the measured energy resolution. After mounting the optical fiber at 100mK, we show that we reach a resolving power of 17 at 402 nm to 10 at 1550 nm from the histogram of single-photon events, with a large (factor ~4) discrepancy between the signal-to-noise and the histogram resolution. We expect that the loss of hot phonons, while down converting the photon energy to quasiparticles, is already showing up at this energy-resolution level. Al MKIDs are particularly sensitive to phonon losses because of the long pair-breaking time. We will present experiments to study the effectiveness of phonon trapping measures.

Speaker: Pieter de Visser (SRON)
• 14
Optical performance of the antenna-coupled lumped-element kinetic inductance detector

The kinetic inductance detector (KID) offers an elegant and convenient solution to building large-format arrays operating at mm-wavelengths. Scaling alternative technology to the large detector counts required for future experiments requires auxiliary multiplexing components that can significantly increase the complexity and cost. Arrays of KIDs require no additional cryogenic multiplexing hardware, only needing a single commercially available low-noise amplifier. A number of experiments are set to serve as the first major demonstrations of KID technology. Of these, the KID design is based on direct free-space absorbing lumped-element KIDs. While effective for single-colour observations, these designs are not directly compatible with the multi-colour on-chip transmission line filtering techniques that have been shown to offer improved focal plane efficiency for wide-band imaging applications. In this presentation we will discuss the recent developments and performance of the antenna-coupled lumped-element KID; a simple KID implementation that permits efficient radiation coupling through a mm-wave microstrip feed. We discuss progress on the design and characterisation of our first prototype lens-coupled twin-slot antenna arrays. We will present results from recent lab-based full optical characterisation and discuss improvements for subsequent design iterations. We will also present preliminary designs and performance of a horn-coupled variant that offers wider bandwidth, reduced parasitic loading, and improved beam systematics. We will present results of initial measurements, and details of our current efforts toward scaling to a full wafer-scale demonstration array operating at 280 GHz.

Speaker: Dr Pete Barry (Argonne National Laboratory)
• Orals LM 006: TT Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Technology transfer, outreach, and dissemination

Convener: Joel Ullom (NIST/University of Colorado)
• 15
Airport passenger security screening: automated detection of concealed threat items with kinetic inductance detector arrays in a passive sub-mm wave scanner.

Real-time video rate imaging and automatic recognition of threats and contraband items that were concealed beneath layers of clothing on moving passengers was recently demonstrated with a prototype passive sub-mm imaging system at Cardiff Airport in the UK. The passengers did not have to divest their outer clothing layers and the instrument was able to distinguish between threat and non-threat items with excellent accuracy in less than the amount of time it takes to pass across the field of view. This level of performance for a passive imaging system is only achievable with low temperature detector systems and, although the financial cost of such systems may be high relative to currently available technology, this is easily offset by the associated benefits; such as increased passenger throughput, reduction of required real estate, avoidance of electromagnetic radiation exposure and, of course, an overall improvement in the passenger experience. Our prototype security imaging system is based on arrays of Aluminium LEKIDs operating at 250mK in a cryogen free cooling platform with compact scanning optics, narrow band optical filters, fast signal processing electronics and a machine learning application for threat detection that was trained with many thousands of marked-up images. We look forward to presenting the latest results of our development.

Speaker: Dr Sam Rowe (Cardiff University)
• 16
Commercially fabricated antenna-coupled Transition Edge Sensor bolometer detectors for next generation Cosmic Microwave Background polarimetry experiment

We report on the development of commercially fabricated multi-chroic antenna coupled Transition Edge Sensor (TES) bolometer arrays for Cosmic Microwave Background (CMB) polarimetry experiments. The orders of magnitude increase in detector count for next generation CMB experiments require a new approach in detector wafer production to increase fabrication throughput.

We describe collaborative efforts with a commercial superconductor electronics fabrication facility (SeeQC-HYPRES, Inc.) to fabricate antenna coupled TES bolometer detectors. We have successfully fabricated an operational dual-polarization, dichroic sinuous antenna-coupled TES detector array on a 150 mm diameter wafers. The fabricated detector array has yields of over 96% and excellent uniformity across the wafer. We have also demonstrated stable detector performance over 4 months. Both RF characteristics and TES bolometer properties are suitable for CMB observations. We successfully fabricated different types of TES bolometers optimized for frequency-multiplexing readout, time-domain multiplexing readout, and microwave SQUID multiplexing readout. We discuss the motivation, design considerations, fabrication processes, test results, and how industrial detector fabrication could be a path to fabricate hundreds of detector wafers for future CMB polarimetry experiments.

Speaker: Dr Aritoki Suzuki (Lawrence Berkeley National Laboratory)
• 4:10 PM
Coffee break Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Orals LM 004: DM Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector Applications

Convener: Marco Vignati (ROMA1)
• 17
Low Temperature Dark Matter Detectors

The dark matter problem has accompanied cosmologist and particle physicist for more than 80 years. Nowadays we have an extremely accurate model of our Universe, but still most of its content eludes our observation. Grasping the nature of this missing matter is of compelling necessity for our understanding. Direct searches aim to detect dark matter particles with Earth-bound detectors. Low-temperature detectors play a crucial role in this challenging hunt, with their capability of accessing interactions of light dark matter particles well below the WIMP-scale. A review of the most sensitive cryogenic approaches to dark matter search and of recent results will be given together with a glance on future prospects.

Speaker: Federica Petricca (Max-Planck-Institut für Physik)
• 18
Technical Performance of a 45cm2 Large Area Photon Calorimeter and Results from a 10gd Surface Search for Light Mass Dark Matter with this Device

We have designed and tested a large area 11-gram photon detector with 45 cm$^2$ surface area and 3.9 eV energy resolution, employing a TES-based readout on a Si absorber. With a 20 $\mu$s rise time due to the fast collection of athermal phonons, this device significantly surpasses both timing and energy resolution requirements of future neutrinoless double beta decay experiments.

Though not optimized for dark matter searches, this device was operated in collaboration with SuperCDMS in a short exposure light-mass DM search on the surface for 10 gram-days. The results of this search illustrate both the immediate and long term scientific potential of athermal phonon sensor technology for light mass dark matter direct detection.

Speaker: Samuel Watkins (University of California, Berkeley)
• 19
SubGeV Dark Matter searches with EDELWEISS

The EDELWEISS collaboration is performing direct searches for light Dark Matter particles using cryogenic germanium detectors equipped with a charge and thermal signal readout. This versatile and highly performing technology opens new possibilities for searches for signals in the subGeV region, involving either electrons or nuclear recoils. This is attested to by results on Axion-Like Particles in the keV range, and by the attainment of the first sub-GeV spin-independent dark matter limit based on a germanium target. The search has been extended to Strongly Interacting Particles (SIMP) down to 45 MeV by exploiting the Migdal effect. New results on SIMPs with spin-dependent interactions will also be presented. Future developments will be discussed.

Speaker: Claudia Nones (CEA/IRFU)
• 20
Search for light dark matter with the CRESST~III experiment

CRESST (Cryogenic Rare Events Search with Superconducting Thermometers) is a long-standing experiment with cryogenic detectors located at the underground facility Laboratori Nazionali del Gran Sasso in Italy. CRESST-III, the third CRESST experiment generation, is designed to probe the spin-independent Dark Matter(DM)-nucleus cross-section with a world leading sensitivity for low DM particle mass (less than 2GeV/c$^{2}$).
Despite many well motivated theoretical models for light dark matter, a large part of the parameter space for spin-independent scattering off nuclei remains untested for dark matter particles with masses below few GeV/c$^{2}$. CRESST experimental approach is the direct detection, which looks for scattering off nuclei of hypothetical dark matter particles inside a target of ordinary matter.
The CRESST-III experiment adopted scintillating CaWO$_{4}$ crystals of $\sim$25~g as target material for dark matter interactions. Each detector module is constituted by a CaWO$_{4}$ crystal paired with a plate made of Silicon-On-Sapphire for the detection of the scintillation light. Both crystals are equipped with Transition Edge Sensors (TES) and operated as cryogenic calorimeters at a temperature of $\sim$10~mK. The double channel read-out of scintillation light and total energy deposition is foreseen for event-by-event particle identification, a crucial feature for background suppression. In addition, a fully scintillating instrumented holder allows for identification of background events originated on the surrounding surfaces.
CRESST-III Phase 1 was successfully completed in 2018, achieving an unprecedented energy threshold for nuclear recoils. This result extended the present sensitivity to DM particles as light as $\sim$160~MeV/c$^{2}$.
In this contribution, a complete overview of the CRESST-III detectors will be presented, emphasizing the latest DM results and the perspectives of future stages of the CRESST experiment.

Speaker: Michele Mancuso (Max-Planck-Institut für Physik)
• 21
Detailed discussion of the most sensitive microwave receiver for Axion Dark Matter detection

This talk will give an overview of the cryogenic detector for the most sensitive experiment to probe the QCD axion to date, Axion Dark Matter eXperiment, (ADMX). The detector technology includes a dilution refrigerator operated at 90mK and quantum-noise-limited amplifiers which contribute minimally to the system noise temperature thereby increasing the experimental sensitivity to the QCD axion. Using these technologies, ADMX has demonstrated recent success in reaching the so-called (DFSZ) sensitivity covering axion mass ranges from 2.66 to 3.31 μeV which no other axion experiment has achieved to this date. These results have crucial implications for the future direction of ongoing dark matter searches.

• Orals LM 002: MUX Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Detector readout, signal processing, and related technologies

Convener: Omid Noroozian (NASA GSFC)
• 22
Advances in time-division SQUID multiplexing for TES X-ray-microcalorimeter arrays

Time-division multiplexing (TDM) is the most mature readout technology for transition-edge sensor (TES) microcalorimeter arrays. Our TDM architecture is routinely deployed to read out 250-pixel scale TES X-ray spectrometer arrays at synchrotron and accelerator beamlines, in table top X-ray spectroscopy experiments, and at electron beam ion trap (EBIT) facilities in applications ranging from materials science to nuclear physics. We continue to develop TDM to offer expanded capabilities in these applications and as a backup TES readout technology for the 3,168-pixel X-IFU instrument on the Athena satellite mission.
We will present results from a proxy 40-row TDM demonstration using NASA TESs that are within the design envelope under consideration for X-IFU. Since our existing 250-pixel TDM readout systems only have wiring to support 32 physically distinct TDM rows, the experiment read out 32 distinct TDM rows plus eight repeat rows for a total of 40 TDM timing rows, simulating the timing and noise of the true 40-row readout planned for X-IFU. Single-column measurements have a best-fit energy resolution of (1.91 ± 0.01) eV for Al Kα (1.5 keV), (2.10 ± 0.02) eV for Ti Kα (4.5 keV), (2.23 ± 0.02) eV for Mn Kα (5.9 keV), (2.40 ± 0.02) eV for Co Kα (6.9 keV), and (3.44 ± 0.04) eV for Br Kα (11.9 keV). Three-column measurements have a best fit energy resolution of (2.03 ± 0.01) eV for Ti Kα and (2.40 ± 0.01) eV for Co Kα. The demonstrated performance meets the dynamic range, energy-resolution, and crosstalk requirements of X-IFU. Larger scale true 40-row readout demonstrations will be conducted with a kilopixel scale TDM readout system that will come online in 2019.
We also report significant progress reducing crosstalk, with the goal of enhancing TDM performance in applications requiring tens or hundreds of X-ray counts per second per pixel. We will describe recent modifications to our cryostat wiring and SQUID multiplexer chips as well as performance in this regime.

Speaker: Dr Malcolm Durkin (NIST)
• 23
Next-generation microwave SQUID multiplexer for metallic magnetic calorimeters

Today microwave SQUID multiplexing appears to be the most suitable cryogenic multiplexing technique for reading out large-scale detector arrays based on metallic magnetic calorimeters. Here, each detector is read out by a non-hysteretic, unshunted rf-SQUID that is inductively coupled to a superconducting microwave resonator with unique resonance frequency. Due to the magnetic flux dependence of the effective SQUID inductance as well as the mutual interaction between the SQUID and the associated microwave resonator, the detector signal is transduced into a resonance frequency shift of the related microwave resonator which can be measured by standard homodyne or heterodyne detection techniques.

In this contribution, we report on our progress in developing a microwave SQUID multiplexer with 400 channels that is optimized for reading out metallic magnetic calorimeters and that provides a bandwidth of 1 MHz for each detector channel. It covers the frequency range from 4 GHz to 8 GHz which is set by the cryogenic low-noise HEMT amplifier that is used for boosting the multiplexer output signal. Compared to our previous multiplexer version, our latest generation is based on a different type of superconducting microwave resonators which allows for a significantly higher packing density. Moreover, the rf-SQUID is optimized with respect to the magnetic coupling between the SQUID and its input coil to overall enhance the energy resolution of the multiplexer as well as with respect to parasitic couplings, e.g. between the input and the modulation coil used for flux ramp modulation. Furthermore, we discuss the readout power dependence of the shape of the resonance curves, the peak-to-peak frequency shift as well as the overall noise performance of a microwave SQUID multiplexer. Finally, we present an advanced multiplexer model that is able to predict the observed power dependence.

Speaker: Dr Mathias Wegner (Kirchhoff Institute for Physics, Heidelberg University)
• 24
Updates of frequency domain multiplexing for the X-ray Integral Field Unit (X-IFU) on board the Athena mission

We are developing the frequency domain multiplexing (FDM) read-out of transition-edge sensor (TES) microcalorimeters for the X-ray Integral Field Unit (X-IFU) instrument on board of the future European X-Ray observatory Athena. The X-IFU instrument consists of an array of $\sim$3000 TESs with a high quantum efficiency (>90 % at 7 keV) and spectral resolution $\Delta E$=2.5 eV @ 7 keV ($E/\Delta E\sim$2800).

FDM is the baseline readout system for the X-IFU instrument. In FDM, TESs are coupled to a passive LC filter and biased with alternating current (AC bias) at MHz frequencies. Each resonator should be separated beyond their detector thermal response (< 10 kHz) to avoid crosstalk between neighboring resonators. To satisfy the requirement of the X-IFU, a multiplexing factor of 40 pixels/channel in a frequency range from 1 to 5 MHz required.
Using high-quality factor LC filters and room temperature electronics developed at SRON and low-noise two-stage SQUID amplifiers provided by VTT, we have recently demonstrated good performance with the FDM readout of Mo/Au TES calorimeters with Au/Bi absorbers. We have achieved a performance requested for the demonstration model (DM) with the single pixel AC bias mode. We have also demonstrated 14-pixel multiplexing with an average energy resolution of 3.3 eV, which is currently limited by non-fundamental issues related to FDM readout in our current lab setup.

In this paper we report on the concept of the focal plane assembly, their requirements, detector performance under FDM scheme, recent results from pre-demonstration model setup and future prospect.

Speaker: Dr HIROKI AKAMATSU (SRON Netherlands Institute for)
• Poster session: Inauguration with buffet (sponsored by IEEE-CSC) Piazza Città di Lombardia

Piazza Città di Lombardia

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Tuesday, July 23
• Orals LM 001: NOVEL Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector Development and Physics

Convener: Kent Irwin (Stanford)
• 25
Superconducting Nanowire Single-Photon Detectors (INVITED)

Superconducting nanowires have demonstrated remarkable performance in terms of efficiency, jitter, dark counts, and reset time. As a result, they have found application in fields ranging from deep-space communications to quantum communications. And recent discoveries have shown remarkable advances in the important performance parameters. However, a number of key developments remain either not fully understood, or remain to be applied to real-world uses. Among them, the development of large-area arrays for use in spectroscopy and imaging, and the development of sensitivity across a wider range of optical bandwidth.

In this talk, I will review recent developments in the field, focussing in particular on the interesting new role that the device microwave environment plays in device performance. I will also present some opportunities for integration of superconducting electronics with the nanowires. Finally, I will comment on opportunities for future work.

Speaker: Prof. Karl Berggren (MIT)
• 26
Intrinsic dark counts in superconducting nanostrip single-photon detectors: the role of multiple fluctuation events in NbN and NbTiN

Superconducting Nanostrip Single-Photon Detectors (SNSPDs) are promising devices in many fields ranging from single-photon source characterization to optical communication and quantum cryptography. An important feature of SNSPDs is their low dark count rate (DCR), that increases close to the critical current where the detection efficiency is higher. In such a region DCR is dominated by a spontaneous resistive-state formation. The investigation of the origin of DCR toward optimization of SNSPD performances is crucial. Phase slip switching events have been considered recently as possible sources of dark counts in SNSPDs: a phase slip event is any process leading to a quantized phase change of the order parameter by 2p able to produce a finite voltage across the strip. Phase slip events include single vortices crossing an edge barrier and vortex-antivortex pairs splitting under the action of the Lorentz force driven by the bias current. In this work, we investigate phase slip events in 2D-NbN and NbTiN nanostripes, e,g, 5 nm thick and 80 nm wide. These materials are of great interest and widely used in SNSPD applications where very low dark count rates are requested. We measure the switching current distributions in a wide interval of temperatures from 6 K down to 0.3 K. The standard deviations of the switching distributions show an extended region at high temperatures where Multiple Phase Slip (MPS) switching events occur. This is probably related to a decreasing of the switching current and an increasing of the electron and phonon capacities: both phenomena cause a lower dissipation during the phase slip event. In this temperature region the width of the switching distribution, and therefore the DCR, is considerably reduced down to values below those observed at the lowest temperature. Finally, we also quantify the energy scale of the fluctuation phenomena. The proposed experimental approach may result in a powerful tool for the diagnostic of SNSPD operation mode.

Speaker: Dr Loredana Parlato (Dip. di Fisica, Università degli Studi di Napoli ‘Federico II’, Napoli, Italy and CNR – Institute of Superconductors, Innovative Materials and Devices, Napoli, Italy)
• 27
Nanowire Detection of Photons from the Dark Side

In recent years, the development of fast and low-dark-count single-photon detectors for photonic quantum information applications promise a radical improvement in our capacity to search for dark matter. The advent of superconducting nanowire detectors, which have fewer than 10 dark counts per day and have demonstrated sensitivity from the mid-infrared to the ultraviolet wavelength band, provides an opportunity to search for bosonic dark matter in the neighborhood of 1 eV. These detectors are simple to fabricate and operate, and can be combined with gas cells, dielectric stacks, or combinations of these structures in cryogenic targets, optimized for dark matter absorption. Furthermore, superconducting nanowires can be used as both target and sensor for direct detection of sub-GeV dark matter [1].
In this work, we will combine resonator systems and quantum large-area single-photon detector, to establish a novel paradigm to look for dark matter with rest mass energies in the range of meV to 10 eV. Inherently resonant systems at these energies—narrow molecular absorption transitions [2] and periodically layered dielectric stacks [3] —bring with them a range of advantages: selectivity, control, and natural background reduction. We demonstrate high-performance 400 by 400 μm large-area tungsten-silicide nanowire prototype with 0.8-eV energy threshold with more than 90 thousand seconds of exposure, which showed no dark counts. The future experiment should enable probing new territory in the detection landscape, establishing the complementarity of this approach to other existing proposals.

Speaker: Dr Ilya Charaev (Massachusetts Institute of Technology)
• 28
Small Array of Low Frequency Readout Quantum Capacitance Detectors

The Quantum Capacitance Detector (QCD) is a new high-sensitivity direct detector under development for low background applications such as far-infrared spectroscopy from a cold space telescope. The QCD has demonstrated an optically-measured noise equivalent power of 2x10-20 W Hz-1/2 at 1.5THz, making it among the most sensitive far-IR detectors systems ever demonstrated, and meeting the requirements for spaceborne spectroscopy. The QCD has also demonstrated single photon detection and counting of 1.5THz radiation. Up to this point, a readout frequency of the order of 2.8GHz has been used. For spaceborne applications, a reduction of readout frequency is desired in order to minimize the readout power requirements. To that effect, we have fabricated and tested a 5x5 array of Quantum Capacitance Detectors with pixel readout frequencies between 613 and 648MHz. There were 4 different detector designs in the array. We have characterized the array under optical illumination with 1.5THz radiation. The measured Noise Equivalent Powers measured under 10-19W of optical loading varied between 2x10^-20 and 6x10-20W/Hz^1/2.

Speaker: Dr Pierre Echternach (Jet Propulsion Laboratory)
• Orals LM 005: QUANTUM Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector for quantum technologies and other frontiers

Convener: Roberto Cristiano (CNR-SPIN)
• 29
Superconducting nanowire single photon detectors for quantum information

Quantum information technology has turned to be a bullet train supported by many countries (EU, USA, UK, JP and CN). The quantum information process (QIP) involves quantum sources, quantum manipulation tools as well as quantum detectors. Since the photon (of visible and near infrared wavelengths) is one of the most popular quanta to play, single photon detectors (SPDs) play an irreplaceable role in QIP. As a novel SPD, superconducting nanowire single photon detector (SNSPD) surpasses the semiconducting SPDs with many merits, such as high detection efficiency, low dark count rate, low timing jitter, higher counting rate etc. SNSPDs have advanced various QIP experiments in the past decade. Now you may buy the commercial SNSPD systems including the cryogenics from several start-up companies. In this talk, we will present the latest results of SNSPDs developed by SIMIT and the applications in QIP (quantum information, QKD, quantum computation etc.).

Speaker: Prof. Lixing You (Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences (SIMIT, CAS) )
• 10:15 AM
Coffee break Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Orals LM 005: QUANTUM Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector for quantum technologies and other frontiers

Convener: Roberto Cristiano (CNR-SPIN)
• 30
Granular aluminum – a versatile material for superconducting detectors and quantum circuits

Granular aluminum is an intriguing superconducting material, which has recently been receiving increasing attention in the superconducting quantum bits (qubits) and detectors communities. Among its key features are a tunable kinetic inductance up to nH/sq, amenable nonlinearity, and low microwave frequency losses [1,2,3]. Furthermore, quasiparticle relaxation times on the order of ~s have been recently observed [1].
We will present our recent results on granular aluminum quantum circuits [4], and discuss how superconducting qubits combined with fast readout electronics could be utilized as ultra-sensitive low temperature detectors.

[1] L. Grünhaupt et. al, Phys. Rev. Lett. 121, 117001 (2018)
[2] N. Maleeva et al., Nat. Commun. 9, 3889 (2018)
[3] F. Valenti et al., Phys. Rev. Appl. (in press), Preprint at: http://arxiv.org/abs/1810.12341
[4] L. Grünhaupt & M. Spiecker et al., Nat. Mater. (in press), Preprint at: http://arxiv.org/abs/1809.10646

Speaker: Lukas Grünhaupt (Karlsruhe Institute of Technology)
• 31
High-Efficiency Superconducting Single Photon Detectors for Quantum Information Processing

Superconducting single-photon detectors have become the preferred technology for applications that require high detection efficiency, ultrafast timing performance and low noise for wide spectral sensitivity spanning UV to IR spectrum. The wide range of applications such as fundamental tests of quantum mechanics, fluorescence microscopy, optical communication and quantum computing, also requires various performance benchmarks which cannot be achieved in one single optimized detector. As a result, different technologies have been pursued with the goal of developing the ideal detector for specific applications. In our group, we have focused on two superconducting single-photon detectors: superconducting nanowire single-photon detectors (SNSPDs) and transition-edge sensors (TES).
I will review the progress on the development of the single-photon detectors tailored for specific applications, in our group. Materials investigations as well as device design were pursued for detector optimization for different applications such as: fundamental tests of quantum mechanics [1], characterization of optical quantum network components [2], ion trap integration for quantum information processing [3], advanced neuromorphic computing platforms [4], exoplanet spectroscopy and molecular spectroscopy in mid-infrared [5].

[1] Lynden K. Shalm et al. Phys. Rev. Lett. 115, 250402 ( 2015)
[2] Gerrits, T., et al., Optics Express, 2018. 26(12): p. 15519-15527.; Levine, Z.H., et al., Journal of the Optical Society of America B, 2012. 29(8): p. 2066-2073.
[3] D. H. Slichter et al. Optics Express Vol. 25, Issue 8, pp. 8705-8720 (2017)
[4] J. M. Shainline, et al., Phys. Rev. Applied 7, 034013 (2017)
[5] Li Chen, et al. Optics Express , 26, 14859 (2018)

• 32
Superconducting single photon detectors integrated on crystalline silicon carbide

Silicon carbide (SiC) is among the most promising optical material for the realization of classical and quantum photonics, due to the simultaneous presence of quantum emitters and a non-centrosymmetric crystal structure. In recent years, progress have been made in the development of SiC integrated optical components making this a mature platform for the implementation of quantum experiments on chip. Toward this scope, the realization of a single photon detector that can be implemented on top of a photonic circuit is essential to achieve a monolithic integration of all the fundamental building blocks required for photonic quantum technologies. Thanks to a new measurement approach that makes use of two alignment mirrors and a single-mode fiber array , here we characterize electro-optically SNSPDs realized on top of 3C SiC using NbN deposited by DC magnetron sputtering. This alignment approach allows the testing of multiple SNSPDs fabricated on top of less fabrication-friendly materials, without the use of expensive and bulky cryogenic positioners. The 3x3 (µm)^2 active area of the realized SNSPD allowed a quasi-saturated detection efficiency at telecom wavelengths at the operating temperature of 2.9K, meaning that high detection efficiency can be obtained by the engineering of the optical system. This is a further step towards the realization of photonic circuit using SiC as monolithic platform for large quantum experiments, interfacing solid-state emitters, reconfigurable linear component and efficient single photon detectors.

Speaker: Dr Francesco Martini (CNR-IFN)
• Orals LM 003: BOLO ARRAY Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector fabrication techniques and materials

Convener: Erik Shirokoff (University of Chicago)
• 33
Kilopixel-Scale Arrays of Kinetic Inductance Detectors on 150 mm Diameter Substrates for the TolTEC Millimeter-Wave Polarimeter

Kinetic Inductance Detectors (KIDs) carry the promise of a truly scalable detector solution, capable of filling the ambitiously large and densely populated focal planes envisioned for future sub-millimeter and millimeter-wave instruments. As part of our effort to realize their full potential, we have developed and fabricated the first kilopixel-scale arrays of KIDs on 150 mm diameter silicon on insulator (SOI) substrates. These initial arrays are being produced for TolTEC -- a new millimeter-wave imaging polarimeter being constructed for the 50-meter Large Millimeter Telescope (LMT). TolTEC uses dichroic filters to define three physically independent focal planes for observations at bands centered at 1.1, 1.4, and 2.0 mm. Each focal plane is filled by a single monolithic detector array fabricated on a 150 mm diameter wafer, and together the three arrays comprise 7,000 polarization sensitive KIDs. Every spatial pixel consists of two detectors, each sensitive to two orthogonal linear polarizations. These devices use a combination of TiN/Ti/TiN multilayer films and thick aluminum films to engineer optimal performance tuned to the loading and observing conditions expected for each band of TolTEC. Here we review the lumped element resonator design, detector optimization, and optical coupling scheme. Furthermore, we describe the integration and layout of thousands of these devices into individual large-scale arrays, which are read out with multiplexing factors of 500--700. We illustrate the design and integration of an entire focal plane module including the micromachined silicon-platelet feedhorns and optical coupling components, the microwave readout interface, and the thermomechanical design. We present the latest laboratory measurements and characterization of these full-sized detector arrays, including the fully-realized 2,000 pixel (4,000 detector) 1.1mm band module, and compare their measured performance to that predicted by theoretical models and simulations.

Speaker: Jason Austermann (University of Colorado-Boulder & NIST-Boulder)
• 34
Design and performance of the BICEP Array receivers

The inflationary scenario generically predicts the existence of primordial gravitational waves, though over a wide range of amplitudes from slow-roll to multi-field models. The presence of these tensor perturbations at the last scattering surface imprinted the cosmic microwave background (CMB) polarization with a unique parity-odd “B-mode” pattern at 1-degree angular scale. The BICEP/Keck (BK) Collaboration targets this primordial signature, which is parametrized by the tensor-to-scalar ratio “r”, by observing the polarized microwave sky from the exceptionally clean and stable South Pole environment. Attempting to observe the primordial B-mode signal requires an instrument with exquisite sensitivity and tight control of systematics as well as a wide frequency coverage in order to disentangle the primordial signal from the Galactic foregrounds.

BICEP Array represents the "Stage-3" instrument of the BK program and it comprises four BICEP3-class receivers observing at 30/40, 95, 150 and 220/270GHz. The 30/40GHz receiver will be deployed at the South Pole during the 2019/2020 austral summer. The full instrument is projected to reach σ(r) < 0.005 by the end of a five years observation campaign with a 30000+ full detectors count. In this talk I will give an overview of the instrument, highlighting the design features in terms of cryogenics, magnetic shielding, detectors and readout architecture. I will also report on the integration and tests that are ongoing with the first receiver at 30/40GHz as well as the design upgrades we implemented for the more challenging 10k-detectors 150GHz receiver.

Speaker: Dr Alessandro Schillaci (Caltech)
• 35
SWIPE multi-mode pixel assembly design and beam pattern measurements at cryogenic temperature

Detecting the polarization of the cosmic microwave background (CMB) represents the best technique to study physical phenomena happening a split-second within the big bang, thus testing the standard cosmological model. In this framework the Short Wavelength Instrument for the Polarization Explorer (SWIPE) aims at the measurement of CMB polarization at the largest angular scales, where cosmic inflation left its imprint in the form of B-modes and E-modes patterns of the linear polarization field.

SWIPE is a cryogenic large aperture polarimeter which will observe 25\% of sky during a two-weeks-long circumpolar stratospheric balloon mission, thanks to 326 multi-mode bolometers cooled to 0.3 K and covering 3 frequency bands centered at 140 GHz, 220 GHz and 240 GHz.

The detectors are fed by a single large-diameter (500 mm) plano-convex lens, cooled at 1.6 K, coincident with the cold aperture stop. The lens is coupled to multi-mode feed horns (28° FWHM), collecting a total of 8800 modes on the bolometers. The bolometer thermistors are Transition Edge Sensors (TES) made of a Ti/Au bilayer with $T_c$ tuned to operate in the 500-550 mK range. The TESs are thermally coupled to a large (10 mm diameter) spider-web absorber, made of Bi/Au coated $Si_3N_4$ wires, with a mesh size of 250 $\mu$m.

The pixel assembly has been tested at the bolometer base temperature of 350 mK, inside a custom cryogenic testbed, looking at a Gunn oscillator (140 GHz) in the far field.
We have developed custom cryogenic neoprene absorbers, in addition to a stack of standard metal meshes low-pass filters, so that the background on the detector is reduced at a level similar to the in-flight one, allowing to measure the full antenna beam. Once corrected for vignetting, the measured FWHM is consistent with the expected one.

Speaker: Fabio Columbro (ROMA1)
• Orals LM 001: MACRO Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector Development and Physics

Convener: Lucia Canonica
• 36
Large calorimeters

Large low temperature detectors are widely used in nuclear and particle physics, from Dark Matter Searches to Double Beta Decay and, more generally, in rare event searches.
The ability to construct large calorimeters from a wide variety of materials is one of the important advantages of this technology.
The possibility - in addition to the heat- to use a second readout channel (scintillation light or ionization charge) in order to disentangle the signal over the background is nowadays deeply exploited by most of the experiments.
This talk will address the main practical challenges related to these detectors, with a summary of the main recent achievements and a prospective for the future.

Speaker: Dr Stefano Pirro (INFN - Laboratori Nazionali del Gran Sasso)
• 37
Cryogenic light detectors for background suppression: the CALDER project.

Background rejection plays a key role for experiments searching for rare events, like neutrino-less double beta decay and dark matter interactions.
Among the several detection technologies that were proposed to study these processes, cryogenic calorimeters stand out for the excellent energy resolution, the ease in achieving large source mass, and the intrinsic radio-purity. Moreover, they can be coupled to a light detector that measures the scintillation or Cherenkov light emitted by interactions in the calorimeter, enabling the identification of the interacting particle by exploiting the different light emission. This feature allows to disentangle signal events from background produced by all the other interactions (mainly alpha particles) that, otherwise, would dominare the region of interest, preventing the achievement of a high sensitivity.

The technology for light detection must ensure an RMS noise resolution lower than 20 eV, a wide active surface (several square cm), a fast time response and a high intrinsic radio-purity. Furthermore, the detectors have to be multiplexable, in order to reduce the number of electronics channels for the read-out, as well as the heat load for the cryogenic apparatus. Finally they must be characterized by a robust and reproducible behavior, as next generation detectors will need hundreds of devices. None of the existing light detectors satisfies all these requests.
In this contribution I will present the CALDER (Cryogenic wide-Area Light Detectors with Excellent Resolution) project, a recently proposed technology for light detection which aim to realize a device with all the described features. CALDER will take advantage from the superb energy resolution and natural multiplexed read-out provided by Kinetic Inductance Detectors (KIDs).

In this contribution I will present the achievements of the CALDER R&D activities and the last results obtained with the final 5x5 square cm light detector.

Speaker: Nicola Casali (ROMA1)
• 1:00 PM
Lunch break Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Orals LM 002: CRYO Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Detector readout, signal processing, and related technologies

Convener: Philippe Camus (CNRS)
• 38
The AMoRE-II Cryostat

The advanced Mo-based rare process experiment (AMoRE) is an international project to search for neutrinoless double beta decay (0νββ) of 100Mo using a large-scale low temperature detector. The project employs scintillating molybdate crystals for high-resolution detection of phonon and scintillation signals with MMC readouts at mK temperatures. AMoRE-II, the second phase of the project, is currently being prepared and will readout/operate 200 kg of molybdate crystals comprised of enriched 100Mo double-beta decaying isotopes. We report on the design and fabrication status of the AMoRE-II cryostat. The mass of the detector tower containing the crystals, copper frame, and lead and copper shields is about 3 ton. The detector tower has a mechanically soft thermal connection to the 1-m diameter mixing chamber plate of the cryostat, and has its own mechanical support system from outside of the cryostat. The system includes a dilution refrigerator, three pulse tube refrigerators, and a precooling unit for the detector tower. We will discuss the details of the refrigeration units, the vibration cares and the shield system of the AMoRE-II cryostat.

Speaker: C.S. Kang (Institute for Basic Science)
• 39
The CUORE cryostat: the first sub-10-mK 1-ton scale infrastructure for low temperature detectors

The CUORE cryostat is today’s largest and most powerful dilution refrigerator in the world. Thanks to its cryogenic performance, CUORE is the first bolometric experiment that has been able to reach the one-ton scale. The CUORE cryostat provides up to 6 µW at 10 mK and can cool down to 6.9 mK a mass of about 1.5 ton in a 4 weeks timescale. By offering an experimental volume of 1 m$^3$ and by delivering a uniform and constant sub-10-mK base temperature, the CUORE cryostat marks a fundamental milestone in low-temperature detectors field, opening the path for future ton-scale bolometric and calorimetric experiments searching for rare events. In this talk, we present the CUORE cryogenic infrastructure, with a particular focus on its critical subsystems in terms of cryogenic and noise performance.

Speaker: Vivek Singh (University of California, Berkeley)
• Orals LM 004: NU Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector Applications

Convener: Young-Hamb Kim (Institute for Basic Science)
• 40
The role of low temperature detectors in neutrino physics

Neutrinos are the most abundant fundamental massive particles in nature. Despite that, many of their basic properties are still unknown, e.g. the absolute value of their mass, their mass hierarchy, the eventuality that they coincide with their own antiparticles, and many others. Answering these open questions is of unvaluable importance to discern among theories beyond the Standard Model and to understand our Universe and its evolution.
Neutrinos are also extremely elusive particles, therefore studying their properties requires challenging technologies and huge mass detectors.
Low temperature detectors can give a crucial contribution to this field. Since their first appearance in the neutrino physics scene in 1984, they have experienced an impressive technological progress that makes them extremely appealing devices for competing experiments.
In fact, low temperature detectors play already a leading role in the search for neutrinoless double beta decay, a rare nuclear process that could shed light on the nature of neutrinos. Moreover, competitive experiments using low temperature detectors are just entering the scene for the direct measurement of the neutrino mass. Also, promising projects aiming at the neutrino coherent scattering detection are being developed.
The challenges and the techniques of running and proposed experiments using low temperature detectors will be reviewed in this talk.

Speaker: Monica Sisti (MIB)
• 41
Probing new physics with Coherent Elastic Neutrino-Nucleus Scattering and the future Ricochet experiment

Neutrinos continue to be a source of scientific wonder in nuclear physics, particle physics, and cosmology. Although much has been learned about the properties of neutrinos, much still pleads for more experimental investigation. The measurement of Coherent Elastic Neutrino-Nucleus Scattering (CENNS) has been a holy grail in neutrino physics since its prediction almost 40 years ago, and has now become a burgeoning field of research following its recent discovery by the COHERENT collaboration in July 2017. Following this first detection, the future Ricochet experiment aims at searching for new physics in the electroweak sector by providing the first low-energy and high-precision measurement of CENNS down to the O(10) eV energy-scale, where new physics signatures may arise. These include for instance the existence of sterile neutrinos and of new mediators, that could be related to the DM problem, and the possibility of Non Standard Interactions that would have tremendous implications on the global neutrino physics program. Thanks to a recently awarded ERC starting grant, the collaboration is building a kg-scale cryogenic detector, with outstanding sensitivity to low-energy nuclear recoils, that will be deployed at an optimal nuclear reactor site within the forthcoming Ricochet neutrino experiment. The key feature of the proposed CryoCube detector technology is to combine two target materials: Ge-semiconductor and Zn-superconducting metal, both targeting O(10) eV energy thresholds with unparalleled background rejection capabilities. This talk will review the science reach of the future Ricochet neutrino experiment as well as the ongoing R&D efforts dedicated to the construction of the CryoCube detector array.

Speaker: Mr Julien Billard (CNRS - IPNL)
• 42
NUCLEUS - Exploring coherent neutrino-nucleus scattering with cryogenic detectors

The NUCLEUS experiment aims for the detection of coherent neutrino-nucleus scattering at a nuclear power reactor with gram-scale, ultra-low threshold cryogenic detectors. This technology leads to a miniaturization of neutrino detectors and allows to probe physics beyond the Standard Model of Particle Physics.

We present results from a 0.5g prototype detector, operated above ground, which reached an energy threshold for nuclear recoils of below 20eV. This sensitivity is achieved with tungsten transition edge sensors which are operating at temperatures of ~15mK and are mainly sensitive to non-thermal phonons. These small recoil energies become accessible for the first time with this technology, which allows collecting large-statistics neutrino event samples with a moderate detector mass. A first-phase cryogenic detector array with a total mass of 10g enables a 5-sigma observation of coherent scattering within several weeks.

We identified a suitable experimental site at the CHOOZ nuclear power plant and show muon and neutron background measurements performed there. The operation of a NUCLEUS cryogenic detector array at such a site requires highly-efficient background suppression.

NUCLEUS plans to use an innovative technique consisting of separate cryogenic anti-coincidence detectors against surface backgrounds and penetrating (gamma-, neutron-) radiation. We present first results from prototypes of these veto detectors and their operation in coincidence with a NUCLEUS target detector.

Furthermore, I will present details on a planned extensive R&D program towards a NUCLEUS phase 2 detector array with a total mass of 1kg. Issues that need to be addressed are the TES fabrication reproducibility, detector mass production and readout multiplexing.

The NUCLEUS experiment has been fully funded and we are currently preparing the first-phase cryogenic detector which is scheduled to be commissioned in 2021 at the CHOOZ nuclear power plant.

Speaker: Johannes Rothe (Max-Planck-Institut für Physik)
• 43
Statuts of the HOLMES experiment

The absolute neutrino mass is still a missing parameter in the modern landscape of particle physics. The HOLMES experiment aims at exploiting the calorimetric approach to directly measure the neutrino mass through the kinematic measurement of the decay products of the weakly-mediated decay of 163Ho. This low energy decaying isotope, in fact, undergoes electron capture emitting a neutrino and leaving its daughter nucleus, 163Dy*, in an atomic excited state. This, in turn, relaxes by emitting electrons and, to a considerably lesser extent, photons. The high energy portion of the calorimetric spectrum of this decay is affected by the non-vanishing neutrino mass value. Given the small fraction of events falling in the region of interest, to achieve a high experimental sensitivity on the neutrino mass it is important to have a high activity combined with a very small undetected pile-up contribution. To achieve these targets, the final configuration of HOLMES foresees the deployment of a large number of 163Ho ion-implanted TESs characterized by an ambitiously high activity of 300 Hz each.

This contribution will provide an overview on the status of the major tasks that will bring HOLMES to achieve a statistical sensitivity on the neutrino mass as low as 2 eV: from the isotope production and embedding to the detector production and readout.

Speaker: Mr Marco Faverzani
• 44
The Electron Capture in 163Ho experiment

The goal of the Electron Capture in $^{163}$Ho (ECHo) experiment is the determination of the electron neutrino mass by the analysis of the electron capture spectrum of $^{163}$Ho. The detector technology is based on metallic magnetic calorimeters operated at cryogenic temperature in a reduced background environment. For the first phase of the experiment, ECHo-1k, the detector production has been optimised and the implantation process of high purity $^{163}$Ho source in large detector arrays has been refined. The implanted detectors have been successfully operated and characterised at low temperatures, reaching an energy resolution below 5 eV. High statistics and high resolution $^{163}$Ho spectra have been acquired and analysed in the light of the recent advanced theoretical description of the spectral shape, considering the independently determined and more precise value of the energy available to the electron capture process, $Q_\mathrm{EC}$, and a dedicated background model. We present preliminary results obtained in ECHo-1k so far and discuss the necessary upgrades towards the second phase of the experiment, ECHo-100k. In particular, we focus on the production of large arrays with $^{163}$Ho embedded in the absorbers and on the multiplexed readout.

Speaker: Ms Federica Mantegazzini (Kirchhoff-Institute for Physics, Heidelberg University)
• 4:15 PM
Coffee break Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• Orals LM 002: Review Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Detector readout, signal processing, and related technologies

Convener: Andrea Giachero
• 45
A Review of Superconducting Readout Electronics for Low-Temperature Detectors

Thanks to the continuous advances in nanofabrication the size of superconducting detector arrays, such as those based on TESs or KIDs, is approaching ~ 10^5 – 10^6 sensors, which is driven by the need to provide faster and more sensitive systems. To access the signals from these arrays, suitable technologies are needed to amplify and multiplex the signals at the cold stage to reduce the cold-stage wiring complexity, cost, and thermal loads in the cooling system, while minimally degrading the signal to noise. In this talk, I will provide an overview of some of the more recent readout technologies being developed in our community, such as superconducting parametric amplifiers, kinetic inductance parametric upconverters, and microwave SQUID multiplexers.

Speaker: Dr Omid Noroozian (NASA GSFC)
• Orals LM 004: Review Auditorium G. Testori

Auditorium G. Testori

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI

Low Temperature Detector Applications

Convener: Andrea Giachero
• 46
Readout systems for large arrays of superconducting resonators for astronomical imaging and spectroscopy

Arrays of superconducting resonators are used for astronomical imaging, polarimetry and spectroscopy as well as in other areas requiring sensitive metrology such as quantum sensing and computation. The low loss of superconducting components enables large numbers of these resonators to be read out using frequency division multiplexing (FDM). I will discuss the system requirements and implementation of electronics for different FDM systems including readout of arrays kinetic inductance detectors (KIDs) and transition edge sensors (TES) for imaging polarimetry and spectroscopy. The power and mass/volume requirements for these readout electronics can be a limiting factor to the size of superconducting detector arrays, especially in constrained environments like balloon-borne or space-based platforms. The rapid development of radio frequency digital signal processing for commercial applications such as software defined radio is enabling larger multiplex ratios, lower power dissipation and smaller mass and volume.

Speaker: Prof. Mauskopf Philip (Arizona State University)
• Poster session: Session A Piazza Città di Lombardia

Piazza Città di Lombardia

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
• 47
Optical Performance of SIS Photon Detectors at Terahertz Frequencies

Astronomy and astrophysics have been continuously seeking observing capabilities with higher angular resolution and better sensitivity. Fast photon detection would be one of the key technologies to advance the detector performance, which may improve the signal-to-noise ratio by resolving each photons, or may lead to photon statistics for high precision measurements in photon-counting mode. SIS junctions (or STJ) can be used as single terahertz photon detectors, which exhibit the post detection bandwidth in the order of GHz. Recently we have developed an SIS junction of Nb/Al/AlOx/Al/Nb, which exhibits leakage currents as low as 1 pA at a cryogenic temperature of $T<$0.7 K, where the NEP of $3\times 10^{-17}\;{\rm W/}\sqrt{\rm Hz}$ can be realized.
Following the success, we have integrated the junction to an antenna coupled detector: The detector consists of a twin slot antenna, coplanar waveguide, and a choke filter. The first detector was fabricated using the CRAVITY facility at AIST, which exhibits the low leakage current of 1-2 pA at $T<$0.7 K. The initial photo-response of the detector was evaluated with a blackbody source, and its frequency response was measured with a Fourier transform spectrometer. The experiments are　showing encouraging results towards the photon counting capability. We are planning to cool the detector with a $^4$He single stage sorption fridge, which can realize a high cooling power of 400 $\mu$W. This will enable us to mount the first stage readout electronics adjacent to the SIS to realize high sensitivity, however the cryogenic temperature may be limited to 0.8-1 K. We are modifying the SIS junction design to extend its low leakage feature for this operating temperature.
Smaller junctions with higher critical current densities are also considered for future space-borne applications, to receive supra-THz photons with wider bandwidth. Current achievements and future prospects of SIS photon detectors will be discussed in the presentation.

Speaker: Hajime Ezawa (National Astronomical Observatory of Japan)
• 48
Detailed STJ and MCA Characterization with a Pulsed UV Laser

The response of high-resolution detectors to a short-pulse laser consists of a set of equidistant peaks corresponding to integer numbers of absorbed photons that follow Poisson statistics. Since the laser has a negligible intrinsic line width, the peaks can be used for detailed characterization of the detector and the data acquisition system. We have characterized superconducting tunnel junction (STJ) photon detectors in the UV and soft X-ray range with a pulsed 355 nm laser at rates up to 5000 counts/s. The observed peaks are described by a Gaussian to very high accuracy, with a width between ~1 and ~2 eV FWHM depending on the detector area. For high statistics, centroids can be determined with an accuracy of a few meV over a range of hundreds of eV. This allows identifying non-linearities in the detector and the digitizer that can limit the accuracy of centroid measurements.

Speaker: Dr Stephan Friedrich (Lawrence Livemore National Laboratory)
• 49
Systematic studies of a sapphire bolometer with phonon pulses in the temperature range of 10-100 mK

An experiment to search for neutrinoless double beta decay in $^{124}$Sn has been initiated in India [1]. It is envisaged to use a superconducting tin-based cryogenic bolometer (TIN.TIN) operating at $\sim$10 mK for this purpose. It is important to study various systematics related to the cryogenic bolometer with a relatively simpler and well-studied absorber material before making a superconducting tin bolometer. With this motivation, a cryogenic bolometer is made with a sapphire absorber ($\sim$0.7 g) and indigenously made NTD Ge sensor [2]. A systematic study of the bolometer performance in the temperature range of 10-100 mK is performed with phonon pulses of energy equivalent to 0.3 - 5 MeV. A C++ and ROOT based pulse analysis program is developed implementing Savitzky-Golay filtering technique for analysing the bolometer signal. In this paper, response of the sapphire bolometer to phonon pulses in the temperature range of 10-100 mK will be presented. Performance of the bolometer with the addition of a moderate size tin sample ($\sim$0.6 g) to the sapphire substrate is studied. Response of the bolometer, when tested with a $^{241}$Am-$^{239}$Pu alpha source will be presented. Impact of vibration on the bolometer will also be discussed.

1. V. Nanal, EPJ Web of Conferences 66 (2014) 08005.
2. A. Garai et al. Journal of Low Temperature Physics 184 (2016) 609.
Speaker: Mr Abhijit Garai (Tata Institute of Fundamental Research, Mumbai 400005, India)
• 50
Development of Neganov-Luke light detectors for a rare event experiment

We report on the recent progress in Neganov–Luke light detector (NLLD) development. The electrodes to generate electric field for Neganov-Luke phonon amplification is configured in a pair of comb-shaped Al electrodes fabricated on one side of a silicon wafer served as a light absorber. A metallic magnetic calorimeter (MMC) is adopted to measure the temperature increase of the absorber wafer. The NLLD was implemented with a scintillating crystal for simultaneous detection of heat and light signals. Clear and monotonic amplification of light signals was resulted with the bias voltage incensement across the electrodes. An amplification factor of 7 was obtained with 80 V bias voltage in the light signals while no difference in signal amplitude and noise was found in the heat measurement channel.

Speaker: Dr JA Jeon (Center for Underground Physics, Institute for Basic Science)
• 51
A 32x32 Doped Silicon based matrix read by HEMT/SiGe Cryo-electronics

During the last decade, CEA have started a long term program to achieve the collective realization of a large (32x32 pixels) µCalorimeters camera for X-ray Astrophysics. This camera is based on silicon doped sensors with Composite Tantalum absorber readout thanks to HEMT/SiGe based Cryo-Electronics. The goal of this development is to achieve a spectral resolution of about 2eV@6keV with a thermal budget in the order of 1 µW@50mK for over 4000 pixels.
After some delays in the production, we present our first measurements obtained our first 32x32 sensors matrix.
We measured R(T), noise and spread between pixels. We will present our first Cryo-Electronics MUX based results.

Speaker: Dr Xavier-François Navick (CEA)
• 52
A cross-talk mitigation technique for FDM readout system in the SAFARI instrument

The SAFARI instrument is a diffraction grating and FTS spectrometer on board the SPICA space observatory, designed to achieve the highest-ever sensitivity for line emission in a wide far-infrared band. It will employ sensitive TES (Transition Edge Sensor) bolometer arrays with nearly 4000 pixels with an NEP of 0.2 aW/√Hz.

Frequency Division Multiplexing (FDM) will be used to read out these bolometers. Under FDM each TES is in series with an LC resonator and then in parallel with other pixels. The detectors share a bias line and are readout by a single SQUID amplifier. Each detector is biased at a particular frequency equal to the resonance frequency of the LC it is in series with. The signal at the TES modulates the amplitude of the carrier signal, which is retrieved when demodulated.

We are currently optimizing our FDM by looking into all the subsystems including bolometer arrays, LC resonators, SQUID amplifier and room temperature electronics. The current baseline is to have multiple FDM readout channels, each capable of reading out around 160 pixels with bias frequency range between 1-4 MHz and 16 kHz spacing. This frequency spacing causes substantial electrical cross talk under high optical loading of the detectors. Under these operating conditions the resistance of the detectors is high, thereby broadening the electrical bandwidth. As a result the amount of the current that leaks into the neighboring pixels is not negligible and in order to determine the optical power on each pixel the resistances of the neighboring pixels and their corresponding bias currents need to be considered at the same time.

Here we discuss carrier leakage and quantify its impact on the readout system in the context of the SAFARI instrument. We also present a fast algorithm to calculate the resistance and the current of each pixel in the whole array, despite large carrier leakage and determine the optical load on each individual pixel.

Speaker: Dr Pourya Khosropanah (SRON)
• 53
A cryogenic front-end preamplifier operating at 120K for bolometric detector

A tin cryogenic bolometer detector, TIN.TIN (The INdia based TIN detector), is being developed to study neutrinoless double beta decay in 124Sn [1]. The detector uses a NTD Ge sensor, cooled to 10 mK in a Cryogen Free Dilution Refrigerator [2]. The change in temperature of the absorber due to any incident photon/charged particle is detected by the sensor and the electrical signal is amplified using a low noise differential amplifier. In the present detection system, output signal of the sensor is transmitted using a long shielded twisted pair cables from the 10 mK stage to the amplification system at room temperature. The large time constant due to the sensor resistance (~500MΩ) and cable capacitance lead to deterioration of the electrical pulse. The long transmission cables are also prone to external EMI pickups. Generally, it is desirable to have a front-end amplification stage inside the cryostat to minimize the effect of long cables. In this paper, we present the design and test results of a cryogenic preamplifier operating at 120K. The preamplifier is implemented in source follower configuration using a low noise Si JFET (IF3601). The DC biasing lines of the amplifier are filtered using low pass RC circuits to eliminate supply noise. A NI based DAQ system is used to measure the voltage gain and input voltage noise density of the amplifier. The amplifier is characterized for different drain current and drain to source voltage of the FET. A gain ~ 0.95 with a 3-dB bandwidth over a wide range from DC to 10 MHz is achieved. The input voltage noise density ~ 3 nV/√Hz is obtained at room temperature which further reduces to 2.47 nV/√Hz at 120K. The flicker corner frequency is also observed to be below 60 Hz. The detailed test results of the amplifier for different bias conditions and its effect on the performance of amplifier will be presented.
[1] V. Nanal, EPJ Web of Conferences 66 (2014) 08005
[2] A. Garai et al. Journal of Low Temperature Physics 184 (2016) 609

Speaker: Dr Ashif Reza (Tata Institute of Fundamental Research, Mumbai-400005, India)
• 54

JPL has developed a flexible radio-frequency readout system suitable for a variety of superconducting detectors commonly used in millimeter and sub-millimeter astrophysics, including Kinetic Inductance detectors (KIDs), Thermal KID bolometers (TKIDs), and Quantum Capacitance Detectors (QCDs). Our system avoids custom FPGA-based readouts in favor of commercially available software defined radio and a C++/CUDA programmed GPU to handle real time signal processing. We demonstrate the performances, the stability and the flexibility of the system by showcasing procedures and results obtained in different readout scenarios.

Speaker: Mr Lorenzo Minutolo (Jet Propulsion Laboratory)
• 55
A New Measurement of the 60 keV Transition in Am-241 Decays using Metallic Magnetic Calorimeters

The 60 keV transition in Am-241 decay is one of the most important calibration standards for low energy gamma-rays. The current literature value of 59.5409(1) keV is based on measurements with high-purity Ge detectors and a Tb-161 reference source in 1993, and its 0.1 eV uncertainty gives it significant weight for cryogenic detector calibration. We have re-measured the energy of this transition in Am-241 decays with metallic magnetic calorimeter (MMC) gamma detectors with an energy resolution of 80 eV and demonstrated high linearity and reproducibility. For calibration, we have made a Yb-169 source, whose gamma emissions are known extremely accurately from measurements using crystal spectrometers, through Tm-169(d,2n)Yb-169 at the 88” Cyclotron. We will discuss statistical and systematic uncertainties of the measurements and provide a preliminary recommendation for an improved value of the Am-241 gamma-ray energy.

Speaker: Geon-Bo Kim (Lawrence Livermore National Laboratory)
• 56
A status of CUPID-Mo bolometric experiment to search for neutrinoless double-beta decay of 100Mo

The LUMINEU project has recently set up a technology for the development of high-performance radiopure 100Mo-containing scintillating bolometers, realized in the framework of the R&D activities towards the proposed tonne-scale neutrinoless double-beta decay experiment CUPID aiming at utilization of the existing CUORE infrastructure. Using in particular 100Mo-enriched Li2MoO4 cryogenic detectors, high energy resolution (5-6 keV FWHM at 2615 keV), excellent alpha background rejection (>99.9%) and extreme radiopurity (below 0.005 mBq/kg of U/Th bulk contamination) have been demonstrated in multiple tests with remarkable reproducibility. Moreover, with only 0.06 kg*yr of 100Mo exposure, the measured two-neutrino double-beta decay half-life is one of the most precise values ever reported. As a follow-up of this activity, a demonstrator named CUPID-Mo is collecting data in the Modane underground laboratory in France. CUPID-Mo consists of twenty 0.2-kg 100Mo-enriched Li2MoO4 scintillating bolometers (containing more than 2 kg of 100Mo) to be operated for at least 0.5 yr, providing a sensitivity to 100Mo larger than 1e24 yr. CUPID-Mo is a very important demonstrator for the implementation of CUPID, as the CUPID-Mo detectors follow closely the configuration chosen for the baseline of CUPID.

Speaker: Denys Poda (CSNSM, CNRS/IN2P3)
• 57

As the size and scale of low temperature detector arrays continue to grow, the demands on the cryogenic multiplexing has dramatically increased. The microwave SQUID multiplexer is meant to address this issue by opening the possibility of multiple gigahertz of readout bandwidth per coax pair. With this readout technique, complexity is moved from the cryogenic stages to the room temperature hardware and digital signal processing firmware. With the variety of microwave SQUID multiplexer designs that are being developed at NIST, the signal processing firmware must have sufficient agility to accommodate different numbers of channels, different resonator bandwidths, and different resonator spacings. The necessary flexibility is possible with the advent of high-performance ADCs and DACs integrated with field programable gate arrays (FPGAs).
We will describe our modular firmware infrastructure and how it can be adapted to different microwave multiplexer applications. Our firmware is implemented on a commercial, off-the-shelf data acquisition platform capable of manipulating up to four gigahertz of bandwidth. Depending on the application, we can modify the channelization module to achieve different target resonator bandwidths and spacings. We will discuss the application space of microwave SQUID multiplexers and how that impacts the firmware modules that need to be implemented. This modular firmware architecture for microwave SQUID multiplexers can be ported to a wide variety of Xilinx FPGAs, including the current and future generations of Xilinx’s RFSoCs.

Speaker: Mr Johnathon Gard (University of Colorado)
• 58
Alpha line detection with Nb based and YBCO based superconducting resonators

For high-energy particle detection, we investigated two materials: niobium and a high-temperature superconductor, YBa$_2$Cu$_3$O$_{7-\delta}$. Lumped element kinetic inductance detectors are fabricated with the both superconductors. The both devices detected the alpha line (5.4 MeV) radiated from $^{241}$Am source at 1 K. The energy resolution of the Nb-base detectors was approximately 0.6 MeV and independent from the power of the readout signal, although the decay time strongly depends on the microwave power and vary from 6-2 $\mu$s.
The duration of alpha line signals with the YBCO-resonators were less than 0.1 $\mu$s due to relatively low quality factor (4000-7000) and very fast quasiparticle life time.

Speaker: Dr Masato Naruse (Saitama university)
• 59
An array scalable zero-bias far-IR detector with noise thermometry readout

We report on a new development effort to achieve an array of ultra-sensitive (NEP < 1E-20 W/sqrt(Hz)) far-IR detectors for applications in spectrometers on Origins Space Telescope (OST) or similar low-background platforms. The detector uses a submicron-size hot-electron bolometer (HEB) sensor made from normal metal (non-superconducting Ti) coupled to a planar microantenna. The detector does not require any bias (dc or rf). The Johnson Noise Thermometry using a quantum noise limited microwave amplifier (LNA) allows for the direct read of an increase of the electron temperate caused by the absorbed far-IR radiation. At 50 mK, the NEP is less than 1E-20 W/sqrt(Hz) is expected whereas the dynamic range is 60-100 dB. Multiplexing of a 1000-pixel array is feasible using a single LNA with a bank of narrowband bandpass filters for channel multiplexing.
In this paper, we will present an initial experimental study of the electrical NEP in a 1µm × 1µm detector. A set of superconducting narrow band-pass (Q = 100-1000) and low-pass filters defines the readout bandwidth around the center frequency of 1.5 GHz. A commercial HEMT LNA with the noise temperature T_A ≈ 1 K largely determines the system sensitivity (NEP ≈ 1E-19 W/sqrt(Hz) @ 50 mK). Electrical NEP is measured by sending a dc current through the device and measuring a change of the output noise power caused by the heating. Switching to a quantum noise limited parametric kinetic inductance amplifier will allows us to reach an NEP close to 1E-20 W/sqrt(Hz). The next phase of this work will be using much smaller HEB devices (e.g., 0.5µm × 0.25µm) where NEP = 3E-21 W/sqrt(Hz) is predicted. Because of the very high dynamic range and optical saturating power, various additional higher background or/and higher operating temperature applications of such a sensor are envisioned.

Speaker: Dr Boris Karasik (Jet Propulsion Laboratory)
• 60
Anti-reflection coating to improve the optical quantum efficiency of PtSi MKIDs arrays

The inductor of a microwave kinetic inductance (MKID) directly absorb the incoming photon, a microlens is used to focuses the light onto the inductor. Such an absorber suffers from a low absorption coefficient since most of the light is reflected on the superconductor metal. An anti-reflection layer can be used to lower the reflectance of the surface by creating destructive interference for the reflected light and constructive interferences for the transmitted one. Materials such as SiO2 and Ta2O5 have optical parameters almost constant over a large range of wavelength which allows an almost perfect impedance matching to be achieved. The performance of optical coatings are thickness sensitive and we present simulations results to tune the thickness of the different layers to optimize the absorption into the detectors. We show that a bi-layer of SiO2/Ta2O5 (thickness 98nm/49nm) deposited on top of the PtSi inductor increases the absorption by 30 percent points between 400-1400 nm. We present data of the absorption of PtSi films coated with SiO2/Ta2O5 measured with a spectrometer and finally we give details on the anti-reflection coating deposition and on the integration of this layer into the fabrication process of our 20,000 pixels MEC arrays.

Speaker: Gregoire Coiffard (UCSB)
• 61
Archeological Lead detectors for neutrino physics

Neutrinos play a crucial role in the Standard Model of particle physics, but also in Astrophysics.
The evolution of a massive star strongly depends on the properties of these particles, especially in Supernova explosions. On this subject very few information are available concerning their production, absorption, and scattering processes and elementary aspects of neutrino transport in dense environments.

Furthermore, one extremely relevant topic is the nature of neutrinos, whether they are Majorana or Dirac particles, but also their absolute values. Neutrinoless double-beta decay is among the best probe for the study of these properties.

In this respect, archeological Lead can be an important and active target material for the study of neutrino properties using Lead-based cryogenic detectors. Archeological Lead is a suitable material for rare events investigations, given its excellent radiopurity and its efficient stopping power.

In this work, we will present the performance of a sample of pure archeological Lead operated as cryogenic detector, and we will review its potential as Supernova neutrino detector.
Moreover, we will show the performance a massive PbMoO$_4$ crystal produced from archeological Lead for double-beta decay applications.

Speaker: Dr Luca Pattavina (Laboratori Nazionali del Gran Sasso (Italy) & Technical University of Munich (Germany))
• 62
Atomic Layer Deposition Josephson Junctions for Cryogenic Circuit Applications

Superconducting-insulating-superconducting (SIS) trilayers have been produced for Josephson Junction fabrication by thermal atomic layer deposition (ALD) processes. The trilayers are composed of alternating layers of Ti0.4N0.6/Al2O3/ Ti0.4N0.6, deposited at 450°C, in a thermal ALD reactor on Al2O3-coated silicon. The conformal nature of the ALD process provides excellent step coverage of superconducting and insulating films. The film thickness of a single ALD cycle being one mono-layer, allows us to precisely control the tunnel-barrier insulator thickness by counting the number of ALD cycles during the insulator deposition step. Tunnel-junctions with critical current 500 A/cm2 are reported. Fabrication of Josephson Junctions and progress toward development of a single-element ALD Superconducting Quantum Interference Device (SQUID) will be discussed.

Speaker: Christine Jhabvala (NASA Goddard Space Flight Center)
• 63
Atomic Layer Deposition Niobium Nitride Films for High-Q Resonators

Niobium nitride (NbN) is a useful material for fabricating detectors because of its high critical temperature and relatively high kinetic inductance. In particular, NbN can be used to fabricate nanowire detectors and mm-wave transmission lines. When deposited, NbN is usually sputtered, leaving room for concern about uniformity at small thicknesses. We present Atomic Layer Deposition niobium nitride (ALD NbN) as an alternative technique that allows for precision control of deposition parameters such as film thickness, stage temperature, and nitrogen flow. Atomic-scale control over film thickness admits wafer-scale uniformity for films 4-30 nm thick; control over deposition temperature gives rise to growth rate changes, which can be used to optimize film thickness and critical temperature. In order to characterize ALD NbN in the radio-frequency regime, we construct single-layer microwave resonators and test their performance as a function of stage temperature and input power. ALD processes can admit high resonator quality factors, which in turn increase detector multiplexing capabilities. We present measurements of the critical temperature and internal quality factor of ALD NbN resonators under the variation of various ALD parameters.

Speaker: Calder Sheagren (University of Chicago)
• 64
Broad-band, high-resolution, transition-edge-sensor arrays for x-ray astrophysics

Future x-ray astrophysics experiments require high-fill-factor kilo-pixel arrays of transition-edge sensors (TESs), with very high spectral resolution over a broad range of energies (typically 0.1-12 keV). In this paper we report on Mo/Au TES designs that are being optimized to meet the stringent resolution, count-rate and uniformity requirements of this next generation of space-based instruments, such as the ATHENA X-IFU instrument, as well as for ground-based laboratory astrophysics experiments using electron-beam-ion-traps (EBITs). These pixels are being optimized for DC bias and time-division-multiplexed readout. In particular, we report on the performance of 50 micron TESs in uniform, kilopixel arrays. These TESs are smaller than those of previous generations and lack the noise-mitigation stripes atop the sensor. The strong geometry dependence of the transition shape means that these devices operate in a régime where the small-signal transition parameters (α and β) are significantly larger than those of their striped counterparts, and these higher values are accompanied by higher detector noise. We examine how these very different transition properties, in conjunction with the choice of the inductance of the detector-bias loop, impact various important performance characteristics of the device such as the time constants, energy resolution, linearity, and uniformity in large arrays and compare the measured performance to calculations from small- and large-signal detector models. We report excellent broadband energy resolution, including 1.9 eV at Al-Ka (1.5 keV), 2.2 eV at Co-Ka (6.9 keV), 2.9 eV at Br-Ka (12 keV), and 4.2 eV at Mo-Ka (18 keV). Tests on multiple pixels in a kilopixel array using TDM readout show these pixels have excellent transition-shape and resolution uniformity.

Speaker: Stephen Smith (NASA GSFC / UMBC)
• 65
CCAT-prime: Cosmology with A Six-meter Submillimeter Telescope at Cerro Chajnantor

CCAT-prime is a new 6 m crossed Dragone telescope designed to characterize the Cosmic Microwave Background (CMB) polarization and foregrounds, measure the Sunyaev-Zel’dovich effects of galaxy clusters, map the [CII] emission intensity from the Epoch of Reionization (EoR), and probe star formation and the dynamics of the interstellar medium in Milky Way and nearby galaxies. CCAT-prime will make observations from a 5,600 m altitude site on Cerro Chajnantor in the Atacama Desert of northern Chile. The novel optical design of the telescope combined with a high surface accuracy (<10 micron) and the exceptional atmospheric conditions of the site will enable sensitive broadband, polarimetric, and spectroscopic surveys at sub-mm to mm wavelengths. Prime-Cam, the first light instrument for CCAT-prime, consists of a 1.8 m diameter cryostat that can house seven individual instrument modules. Each instrument module, optimized for a specific science goal, will use the state-of-the-art multichroic transition edge sensor (TES) or kinetic inductance detector (KID) arrays operated at 100 mK, and Fabry-Perot interferometers (FPI) for the EoR science. Prime-Cam will be commissioned with staged deployments to populate the seven instrument modules. The full instrument will consist of 24,000 polarimetric TES bolometers at a combination of 220/270/350/410 GHz, 12,000 TES bolometers at 250/350 GHz coupled with FPIs, and 18,000 polarimetric KIDs at 860 GHz. Prime-Cam is currently being developed, and the CCAT-prime telescope is designed and under construction by Vertex Antennentechnik GmbH to achieve first light in 2021. CCAT-prime is also a potential telescope platform for the future CMB Stage-IV observations.

Speaker: Steve Choi (Cornell University)
• 66
Characterization of a Ti/Au TES with Au/Bi absorber under AC and DC bias

Transition Edge Sensors (TESs) are used as very sensitive thermometers in microcalorimeters aimed at different wavelengths detection. In particular, for soft X-ray astrophysics, science goals require very high resolution microcalorimeters which can be achieved with TESs coupled to suitable absorbers. For many applications there is also need for a high number of pixels which need to be multiplexed in the readout stage. Frequency Domain Multiplexing (FDM) is a common scheme and is the baseline proposed for the ATHENA mission. FDM requires biasing the TES in AC at MHz frequencies. Recently there has been reported degradation in performances under AC with respect to DC bias. In order to assess the performances of TESs to be used with FDM, it is thus of great interest to compare the performances of the same device under both types of bias. This means using two completely different setups and characterization protocols.
We report in this work a preliminary comparison of the characterization of a single pixel with a Ti/Au TES, performed under DC and AC bias in two different facilities. Dynamical parameters and noise are compared in both cases showing compatible results and has allowed definition of protocols for future AC/DC comparison of these devices.

Speaker: Carlos Pobes Aranda (ICMA)
• 67

Advanced ACTPol is the second generation polarization-sensitive upgrade to the 6m aperture Atacama Cosmology Telescope (ACT), which increased detector count and frequency coverage compared to the previous ACTPol receiver. Advanced ACTpol utilizes a new two-stage time-division multiplexing readout architecture based on superconducting quantum interference devices (SQUIDs) to achieve a multiplexing factor as high as 64 (rows) fielding a 2012 detector camera at 150/220 GHz and two 90/150 GHz cameras containing 1716 detectors each. We present the aliasing noise characteristics of the advanced ACTpol receiver as deployed.

Speaker: Mr Patricio Gallardo (Cornell University)
• 68
Characterization of Transition Edge Sensors for Simons Observatory

The Simons Observatory is building both large (6m) and small (0.42m) aperture telescopes in the Atacama desert in Chile to observe the cosmic microwave background (CMB) radiation with unprecedented sensitivity. Simons Observatory telescopes in total will use over 60,000 transition edge sensor (TES) detectors spanning frequencies between 27 and 270 GHz and operating near 100mK.
TES devices have been fabricated for the Simons Observatory by NIST, Berkeley, and commercially by HYPRES corporation. Iterations of these devices have been tested cryogenically in order to inform fabrication of further devices, which will culminate in the final TES designs to be deployed in the field. Designs must be iterated on independently for each fabrication facility and each desired detector frequency.
We present the results of this device testing. A dilution refrigerator system was used to achieve the required temperatures. Measurements were made both with 4-lead resistance measurements and with a time domain SQUID multiplexer system. The SQUID readout measurements include a detailed analysis of I-V curves at various temperatures as well as detector noise measurements. Normal resistance, superconducting critical temperature, saturation power, and thermal properties of the devices are extracted from these measurements.

Speaker: Mr Jason Stevens (Cornell University)
• 69
Charge exchange measurements with neutral hydrogen using the X-ray Quantum Calorimeter (XQC)

X-ray emission from charge exchange between highly-charged ions and neutral atoms forms a significant portion of the emissions from galactic outflows and stellar winds and is an important source of soft X-ray emission in our Solar system. Theoretical modeling of the velocity-dependent partial cross sections for X-ray line emission in charge exchange has so far proven difficult. High-resolution laboratory measurements of X-ray line emissions from charge exchange over a wide range of collision velocities are needed to test and benchmark the various theoretical models currently available.
Our XQC sounding rocket detector system has been modified for efficient use as a detector on the merged beam facility at Oak Ridge National Labs (ORNL). We are using this to take high-resolution spectra of charge exchange between astrophysically relevant ions and neutral H atoms. Any ion of interest can be generated and merged with a neutral H beam with relative velocities adjustable over the entire range of astrophysical interest. We present our initial results and details of the experimental design.

Speaker: Conjeepuram Ambarish (University of Wisconsin-Madison)
• 70
Compact Gamma Spectrometer

Implemented at nuclear facilities, ultra-high-resolution microcalorimeter gamma spectroscopy offers important capabilities for advanced nuclear fuel cycle safeguards. Our goal is to reduce the performance gap between nondestructive and destructive isotopic analysis methods. The improved energy resolution of microcalorimeters can reduce uncertainty in nondestructive isotopic composition measurements of plutonium and other complex nuclear materials. Advancements in large array fabrication, multiplexed readout, electrically-cooled cryostats, signal processing, and data analysis have enabled us to develop an instrument architecture capable of count rates comparable to germanium detectors but with 5-10 times better energy resolution. We are now building a compact gamma spectrometer using a High Precision Devices Model 102 cryostat and Cryomech PT403 pulse tube cryocooler. Larger systems requiring three-phase electrical power and cooling water are unsuitable for installation at many analytical laboratories. This compact air-cooled cryostat system requires only single-phase electrical power similar to a large window air conditioner, and enables many new opportunities for testing and deployment. With 256 pixels and high-bandwidth microwave frequency-division multiplexing, total count rates of over 5000 per second are expected. We will present the design of the compact gamma spectrometer, initial results, and plans for testing in nuclear facilities.

Speaker: Mark Croce (Los Alamos National Laboratory, USA)
• 71
Compact, add-on sub-Kelvin modules extend the working range of 4K mechanical pre-coolers to temperatures below 1K

The technology for low-power sub-Kelvin cooling is is now established and products are available that offer simple operation, with reliable and repeatable performance at relatively low cost. Self-contained, sealed sub-Kelvin modules can be added-on or retro-fitted to low-power mechanical (GM or PT) pre-coolers to extend their operating temperature downwards, from 4K into the sub-Kelvin range. A system using this technology offers fully automated operation requiring little or no cryogenics expertise and superior performance when compared to systems relying on pre-cooling with liquid cryogens. When tested in a liquid-helium-cooled cryostat, tests on more than 30 individual sub-Kelvin modules manufactured over the past two years yielded base temperatures averaging 825±20mK under no load, rising to 858±26mK under an external load of 100µW. Run times (before recycling was needed) were typically ~29±3 hours, though could be as high as 40 hours. With a low-power GM pre-cooler and automated operation, the average operating temperatures of these modules were lower and the run times significantly longer, up to ~100 hours, Highly compact systems offering extended or even continuous operation below 1K, using two sub-Kelvin modules cycled in antiphase under fully automated control, are the next development in this rapidly maturing field.

Speaker: Ms Emily Ronson (Chase Research Cryogenics Ltd)
• 72
Complex beam maps and a fourier optics analysis of a wide field MKID camera

For astronomical instruments, accurate knowledge of the optical pointing and coupling are essential to crosscheck or characterize the alignment and performance of (sub-)systems prior to integration and deployment. The standard technique for this purpose with phase-sensitive heterodyne spectrometer instruments is the complex beam pattern, which describes both the amplitude and phase response of an optical system. The phase response gives the optical path difference and hence describes the curvature of the (spherical) optical wavefront. Previously with direct (phase-insensitive) total power detector systems the beam patterns were typically measured with incoherent thermal sources. The resultant amplitude-only maps could then only be interpreted by a comparison to simulation in the plane of measurement. To extract precisely the pointing and focus position would then require multiple scans along the direction of the beam propagation. In comparison, from a single complex beam pattern map the beam pointing and focus position can be directly determined by fitting the complex beam parameters. The complex beam pattern can additionally be further analyzed, for example by using angular plane wave spectrum Fourier optics or by directly importing into physical optics software. Here we show how the measured complex patterns can be analyzed with Fourier optics and integrated into a telescope model to calculate the on sky beam pattern and telescope aperture efficiency prior to deployment at a telescope. As a test case we present measurements and analysis on complex beam maps from a wide camera at 350GHz, using an array of 880 array of lens-antenna coupled Microwave Kinetic Inductance Detectors.

Speaker: Dr Stephen Yates (SRON)
• 73
Complex impedance of optical transition-edge sensors with sub-microsecond response

Optical transition edge sensor (TES) detectors which can resolve an energy of a single optical photon have proven desirable in quantum information and biological imaging. Optical TESs were designed to have a high detection efficiency at a specific wavelength and has achieved nearly 100 % at the wavelength. They have been proven to have the sensitivity at a wide bandwidth from near-infrared to visible regions. The energy resolution was typically 0.1 to 0.2 eV. Higher energy resolution is required for an application of the TESs in multicolor fluorescence microscopy. A question arising here is if we have reached the theoretical limit of the energy resolution. To calculate the limit, we need to measure parameters such as the temperature sensitivity $\alpha$ and the current sensitivity $\beta$, extracted from the complex impedance.
The optical TES is characterized by: (1) its small size (typically 5 to 10 $\mu$m) to be sensitive to the low-energy photons and (2) a fast response time (< 1 $\mu$s) determined by the heat capacity and weak thermal coupling between electrons and phonons in the detector. To extract $\beta$ of a sub-microsecond TES, the complex impedances need to be measured at high frequencies (> 1 MHz), where the parasitic impedance in the circuit and reflections of electrical signals due to discontinuities in the characteristic impedance of the readout circuits become significant. To reduce the parasitic impedance and the discontinuities, we have replaced legacy twisted cables with coaxial ones and obtained cleaner transfer function of the readout. Figures show the complex impedance of a TES sensitive to MHz-electrical perturbations. We will discuss the theoretical limit of the energy resolution and a possible thermal model of the TES.

Speaker: Dr Kaori Hattori (AIST)
• 74
Cryogenic instrumentation developed for the characterization of advanced CMOS technologies down to 250 mK

The cryogenic systems is becoming vital in R&D activities in many fields ranging from cooled detector integrated electronics to quantum computing systems. Although CMOS technology has been widely studied, current models do not consider transistor behavior at ultra-low temperatures. Developing the necessary instrumentation to characterize transistor structures fabricated in CMOS commercial processes, including a 65nm one, is the aim of this work.
A 4K closed-cycle cryostat has been modified to characterize the samples of interest and it includes a cold-finger with an adapter designed to fit 24-pin ceramic dual in-line packages (C-DIP), chosen based on their high thermal conductivity at ultra-low temperatures. In order to control the cooling rate of the system and achieve different operating temperatures, three thermal stage structures were designed, manufactured and characterized to work on top of the 4K plate at different distances. They yield minimum cooling rates of respectively 0.2K/min, 0.17K/min, and 0.15K/min. This allows for measurements to be performed while sweeping down the operating temperature. The temperature data are monitored and saved using a NI-Labview program interfaced to a Lakeshore temperature monitor. In order to achieve a good tradeoff between the necessary electrical conductivity and the maximum heat transfer allowed by the system, manganin wiring was used inside the closed-cycle cryostat. Since the manganin thermal conductivity varies with temperature, the wiring was performed to enable working below the maximum power dissipation level allowed (~2 or 3 µW) whilst maintaining the temperature stable in the sub-Kelvin regime. The cryostat has four different temperature stages introduced to reduce the heat transfer from the measurement equipment to the device under test. Vacuum connectors and a matrix with triaxial connectors are both used to connect the semiconductor device analyzer (SDA) held at room temperature with the internal connections.

Speaker: Mr Ismael Martínez (National Institute of Astrophysics, Optics, and Electronics (INAOE))
• 75
Data analysis and results for multi-absorbers TES

We have been developing position-sensitive detectors, most recently for the proposed Lynx X-ray observatory currently under study for the next 2020 decadal survey. These detectors, referred to as hydras, are composed of multiple absorbers connected to a single transition-edge sensor (TES), each with a different thermal conductance. Using this technique as a form of thermal multiplexing allows the design of arrays at the scale of a hundred kilo-pixels, while keeping fairly good performance with reasonable read-out electronics. For these detectors a different pulse shape is measured by each of the pixels of the hydra when X-rays are absorbed. It is hence crucial to optimize the process of analyzing the data, to optimally discriminate the events from different pixels, and to provide the best possible energy resolution.

In this work we describe our studies of the characterization of our latest hydra designs. Two different designs are studied, one with 50 $\mu$m and one with 25 $\mu$m absorbers, but in both cases there are 25 pixels per hydra. These have demonstrated a combined (rms) energy resolution $\Delta$E of ~2.5 eV for the small pixels and ~3.4 eV for the large ones at 1.25 keV, which is roughly in agreement with our expectations. We review the different measurements performed in order to characterize the pixels and discuss how the processing had to be adapted in order to properly handle this kind of data, in particular to discriminate between X-ray events in the different pixels.

Speaker: Sophie Beaumont (NASA-GSFC / UMBC)
• 76
dc-SQUID readout scheme with high dynamic range and intrinsic MHz frequency-domain multiplexing capability

Direct-current superconducting quantum interference devices (dc-SQUIDs) are among the most sensitive wideband devices for measuring any physical quantity that can be naturally converted into magnetic flux. Therefore, they are ideally suited, for example, for reading out cryogenic particle detectors such as transition edge sensors or metallic magnetic calorimeters. However, SQUIDs are intrinsically non-linear devices due to their periodic flux-to-output signal characteristics. For this reason, their linear flux range is rather small and for many applications a flux-locked loop (FLL) circuit to linearize the relation between the SQUID input and output signal is employed. Despite the great success of this technique, FLL operation requires feedback wires routed to each SQUID often setting a practical limit for modern multichannel SQUID-systems.
In this contribution, we present a novel readout scheme for dc-SQUIDs that provides linearization of the SQUID output without the need for individual feedback wires. At the same time, it allows for setting up an easy-to-use MHz frequency-division SQUID multiplexer not requiring large on-chip filter elements. Moreover, it significantly increases the dynamic range of the SQUID system. Our readout scheme is based on flux ramp modulation which was originally introduced for linearizing the output signals of a microwave SQUID multiplexer. It relies on applying a sawtooth-shaped flux signal to the SQUID to perform a quasi-continuous measurement of the SQUID characteristic. If the amplitude and repetition rate of the flux ramp is appropriately chosen, the input signal is transduced into a phase shift of the SQUID output which depends linearly on the input signal. We will discuss the basic scheme of this technique as well as a comprehensive suitability study, in particular in the context of reading out our cryogenic particle detectors, demonstrating its intrinsic multiplexing capability.

Speaker: Mr Daniel Richter (Kirchhoff-Institute for Physics, Heidelberg University, Heidelberg, Germany)
• 77
Design of a testbed for the study of system interference in space CMB polarimetry

LiteBIRD is a proposed JAXA satellite mission to measure the CMB B-mode polarization with unprecedented sensitivity ($\sigma_r \sim 0.001$). To achieve this goal, $\sim 4000$ state-of-the-art TES bolometers will observe the whole sky for 3 years from L2. These detectors, as well as the SQUID readout, are extremely susceptible to EMI and other instrumental disturbances e.g. static magnetic field and vibration. As a result, careful analysis of the interference between the detector system and the rest of the telescope instruments is essential. This study in an early phase of the project is particularly important in order to reduce risks and do a sanity-check before final assembly of the whole instrument. We report a plan for the preparation of a cryogenic testbed to study the interaction between the detectors and other subsystems, especially a polarization modulator unit consisting of a magnetically-rotating half wave plate. We also present the requirements, current status and preliminary results.

Speaker: Tommaso Ghigna (University of Oxford)
• 78
Design, simulation and fabrication of highly sensitive cooled silicon bolometer for millimetre wave absorption

Silicon bolometers feature a remarkably high sensitivity when cooled at very low. These devices can be used as polarization sensitive detectors in the field of millimetre-wave radiation imaging and polarimetry, typically in the range 200 to 500 GHz. The radiation absorption is based on Ti/TiN superconducting thin films with an adapted critical superconducting transition temperature (Tc) for mm-wave absorption. This absorber is deposited on a doped silicon thermometer fabricated on silicon-on-insulator (SOI) wafers with Phosphorus or Arsenic doping and Boron compensation. The absorber and thermometer are suspended above an optical cavity in order to have good electrical and optical performances. This device should give a high responsivity (S=dV/dP), typically around 1E11 V/W and a very low noise equivalent power (NEP) of 1E-18 W/Hz^1/2 between 50 and 100 mK. Doped silicon thermometers present non-ohmic behaviors at very low temperature, described by the “hot electron model” (HEM). This model assumes that electron-electron thermal coupling is stronger than thermal coupling between electrons and phonons (lattice), which means that applied electrical power is directly deposited on electron systems rising their temperature compared to the lattice. In this paper, we investigate the simulation of ion implantation and diffusion of dopants profiles in silicon thermometers and compared them to Secondary Ion Mass Spectrometry (SIMS) measurements, then we performed electrical resistance measurements as a function of applied electrical powers “R(P)” at low temperature on fabricated devices showing a good fit with the hot electron model. We show that the HEM is governing the electrical characteristics of the doped silicon thermometer and we show its impact on the electrical sensitivity at very low temperature. Finally, simulation results of absorption, responsivity and NEP are presented for pixels with a pitch of 500 and 1200µm under weak and moderate optical power illumination.

• 79
Designing a Gas Cell Experiment for the Calibration of DESHIMA

The DESHIMA instrument is a wideband submillimeter spectrometer based on a single NbTiN superconducting chip, which is integrated with a dispersive filterbank and Microwave Kinetic Inductance Detectors (MKIDs) sensor array. For the next campaign at the ASTE telescope in Chile, DESHIMA is expected to have an instantaneous bandwidth from 220-440 GHz with 347 channels, achieving a resolution power of f/Δf =500. We present the design of a gas-cel calibration system, that is designed to calibrate the spectrometer in absolute frequency and which can also be used to perform long integration time tests, simulating the detection of faint extra-galactic lines.

The calibration system mainly consists of a gas cell between the spectrometer and a cold load that can be filled with room temperature gas at low pressure. In front of the gas cell is an optical chopper that eliminates 1/f noise and also modulates the spectrometer signal between the gas cell and a another cold load. The spectrometer detects the irradiance from the cold load through the gas cell with certain gas opacity. The absolute frequency can be calibrated by comparing the observed transmission spectrum of the gas and its model spectrum. The pressure in the gas cell can be tuned down to achieve higher gas opacity and smaller detected signal for the long integration time tests.

Speaker: Ms Zhongyue Zhang (Leiden University/TU Delft)
• 80
Detector fabrication development for the LiteBIRD satellite mission

LiteBIRD is a satellite mission designed to measure the polarization of the cosmic microwave background and cosmic foregrounds from 34 to 448 GHz. This experiment aims to measure primordially generated B-mode polarization at large angular scales and will generate a dataset capable of probing many scientific inquiries such as the sum of neutrino masses. The experiment will have three optical telescopes each covering a portion of the entire frequency range. The broad frequency coverage and low optical loading conditions require development of detectors suitable for the mission. The focal plane design is driven by heritage from ground based experiments and will include both lenslet-coupled sinuous antenna pixels and horn-coupled pixels. This detector development and fabrication will take place at UC Berkeley and NIST. We present on current development status as well as future fabrication plans for LiteBIRD.

Speaker: Dr Benjamin Westbrook (UC Berkeley)
• 81
Detector Performance in the Micro-X Telescope

Micro-X is a sounding rocket borne instrument that uses a Transition Edge Sensor microcalorimeter array to perform high-resolution spectroscopy in the X-ray band. This instrument flew for the first time on July 22nd, 2018 from White Sands, New Mexico. An internal calibration source is used to compare data taken during pre-flight integration, flight, and after the successful post-flight recovery. Although a rocket software glitch during the flight led to a failure of the attitude control system so that no time was spent observing the target, these calibration data demonstrate the capabilities of this detector in a flight environment as well as its potential for future flights.

Speaker: David C. Goldfinger (Massachusetts Institute of Technology, Northwestern University)
• 82
Determination of depairing current of superconducting thin films by means of superconducting nanowire resonators

We estimate the depairing current of superconducting nanowire single-photon detectors$^1$ (SNSPDs) by studying the dependence of the kinetic inductance on the bias current. The kinetic inductance is determined by measuring the microwave resonance frequency of resonator-style nanowires$^2$. Bias current dependent shifts in the measured resonant frequency correspond to a change in the kinetic inductance, which can be compared to theoretical predictions. We demonstrate that the fast relaxation model$^3$ described in the literature accurately matches the experimental data, as expected based on the short relaxation time of the superconductor compared to the resonant frequencies of the test devices. This method provides a valuable tool for directly determining the depairing current, since it minimizes reliance on externally measured values. Accurate measurement of the depairing current is extremely useful both for theoretically understanding the detection mechanism in SNSPDs and for estimating the quality of the fabricated nanowires and, ultimately, the yield of potentially large arrays. Finally, experiments show that the accessible fraction of the depairing current, namely the so-called constriction factor$^4$ C which is the ratio between the switching and depairing currents, decreases with increasing temperature.
1- G.N. Gol’Tsman et al., “Picosecond superconducting single-photon optical detector”, Appl. Phys. Lett. vol.79, p: 705 (2001)
2- D. F. Santavicca et al., “Microwave dynamics of high aspect ratio superconducting nanowires studied using self-resonance”, J. Appl. Phys. 119, 234302 (2016)
3- J. R. Clem and V. G. Kogan, “Kinetic impedance and depairing in thin and narrow superconducting films”, Phys. Rev. B vol.86, 174521 (2012)
4- A. J. Kerman et al., “Constriction-limited detection efficiency of superconducting nanowire single-photon detectors”, Appl. Phys. Lett. 90, 101110 (2007)

Speaker: Simone Frasca (EPFL)
• 83
Developing a Large -Scale Cryogenic System for the Simultaneous Operation of Three Detector Focal Planes in TolTEC, A New Multichroic Imaging Polarimeter

TolTEC is an upcoming multiwavelength imaging polarimeter designed to fill the focal plane of the 50-m diameter Large Millimeter Telescope (LMT). Combined with the LMT, TolTEC will offer high angular resolution (5”-10”) simultaneous, polarization-sensitive observations in three wavelengths: 1.1, 1.4, and 2.0 mm. Additionally, TolTEC will feature mapping speeds greater than 2 deg$^2$/mJy$^2$/hr, thus enabling wider surveys of large-scale structure, galaxy evolution, and star formation. These improvements are only possible through the integration of approximately 7000 low-noise, high-responsivity superconducting Lumped Element Kinetic Inductance Detectors (LEKIDs). To utilize three focal planes of detector arrays requires the design, fabrication, and characterization of a unique, large-scale cryogenic system. Based on thermal models and expected photon loading, the focal planes must have a base operational temperature below 150 mK. To achieve this base temperature, TolTEC utilizes two cryocoolers, a Cryomech pulse tube cooler and an Oxford dilution refrigerator, to establish four thermal stages: 45 K, 4 K, 1 K, and 100 mK. During the design phase, we developed an object-oriented Python code to model the heat loading on each stage as well as the thermal gradients throughout the system. This model has allowed us to improve thermal gradients in the system as well as locate areas of poor thermal conductivity prior to ending a cooldown. The results of our model versus measurements from our cooldowns will be presented along with a detailed overview of TolTEC’s cryogenic system. We anticipate TolTEC to be commissioned at the LMT in Fall 2019.

Speaker: Nat DeNigris (University of Massachusetts Amherst)
• 84
Development of a 350-GHz Dual-Polarization On-Chip Spectrometer

Broadband imaging spectrometers are playing an increasingly important role in terahertz astronomy. As is well known, microwave kinetic inductance detectors (MKIDs) use frequency-domain multiplexing (FDM) that allows thousands of pixels to be read out through a single coaxial transmission line. Based on Al MKIDs incorporating a Nb/SiO2/Nb thin-film microstrip-line filter bank, we are developing a 350-GHz dual-polarization on-chip spectrometer with a frequency resolution of about 100. Detailed simulation and measurement results will be presented.

Speaker: Prof. LI Jing
• 85
Development of a closed-cycle miniature dilution refrigerator for a fast-cooldown 100 mK detector wafer test cryostat

The forthcoming generation of Cosmic Microwave Background polarization observatories are developing large format detector arrays which will operate at 100 mK. Given the volume of detector wafers that will be required, fast-cooldown 100 mK test cryostats are increasingly needed. A miniature dilution refrigerator (MDR) has been developed for this purpose and is reported. The MDR is pre-cooled by a double stage $^3$He/$^4$He Chase Research Cryogenics ''Berkeley-style'' sorption refrigerator. The test cryostat based around this MDR will enable fast cooldown to 100 mK to support rapid feedback testing of detector wafers fabricated for the Simons Observatory. The MDR has been designed so as to be retrofitted to existing CRC10 sorption coolers, reducing the base temperature from 250 mK for the new generation of detectors. This configuration will meet the cryogenic requirements for single-wafer testing, providing $\sim$5-10 $\mu$W of cooling power for several hours. The system operates in a closed cycle, therefore avoiding external gas connections and cold o-rings. No moving parts are required, with the system operated entirely by heaters. It is possible to fully automate the cycling of each stage in order to provide ''push-button'' cooldown to 100 mK. Furthermore, the architecture of the system that has been developed is such that it could easily be implemented for other low-temperature detector applications requiring similar cooling powers.

Speaker: Ms Susanna Azzoni (The University of Manchester)
• 86
Development of a Reconfigurable Readout for Superconducting Arrays

New fully integrated digital signal processing technology called Radio
Frequency System on a Chip (RFSoC) developed for communications and
defense applications will set the standard for future astronomical
instruments which utilize superconducting arrays of kinetic inductance
detectors (KID), Transition edge sensors (TES), and nanowire single
photon detectors (SNSPD). The RFSoC combines a fabric of
reconfigurable logic, high speed input/output digitizers, and a
microprocessor all onto a single integrated chip. This dramatically
reduces the size, weight, and power of the system while simultaneously
increasing the instantaneous bandwidth. In parallel the open source
community has developed a Python interface for high performance SoCs
which allows for rapid software development. Taking advantage of this
product of Moore's law and leveraging previous work we have begun
firmware development on the ZCU111 RFSoC evaluation board. We report
on the algorithms, firmware, and software implementation as well as
preliminary measurements with superconducting arrays. We will also
discuss the potential for RFSoC-based readouts as a platform for
balloon-borne and space based telescopes.

Speaker: Mr Adrian Sinclair (Arizona State University)
• 87
Development of a TiAu TES microcalorimeter array as a backup sensor for the Athena/X-IFU instrument

Athena is a future X-ray observatory led by ESA, to be launched in the early 2030s. The X-ray Integral Field Unit (X-IFU) instrument on-board Athena provides spatially-resolved high resolution spectroscopy of 2.5 eV with a large array of Transition Edge Sensor (TES) microcalorimeters. The main sensor is a MoAu bi-layer TES array provided by NASA-Goddard. Pixels are read out with a frequency-division multiplexing (FDM) readout system developed by SRON, using VTT SQUIDs. Extensive research collaborations between NASA-Goddard and SRON on TES design optimizations under FDM readout have resulted in new TES design rules such as: low resistivity, moderately high ohmic resistance by changing the TES aspect ratio and no metal strips on the bi-layer.
We have been developing a TiAu bi-layer based TES array as a backup option for the Athena/X-IFU. We have improved our detector fabrication procedure along the design principles. The bi-layer thickness is 35 nm Ti/200 nm Au and has ohmic resistances that vary from 50 to 150 mOhm depending on the aspect ratios. An X-ray absorber is made of 2.4 um thick Au that is thermally coupled to the TES via small stems attached to the sides of the TES. We observed Tc of 110 mK and as a preliminary result, 2.4-2.8 eV energy resolutions have been achieved with some TES pixels under the AC bias (to be reported by E. Taralli et al at this conference), showing that our TiAu TES array has a potential to be a real backup sensor for the X-IFU. In this paper, we will present our successful fabrication results and discuss on possibilities of further improvements.

Acknowledgment: This work is partly funded by European Space Agency (ESA) under ESA CTP contract ITT AO/1-7947/14/NL/BW, and is partly by the European Union’s Horizon 2020 Programme under the AHEAD project with grant agreement number 654215.

Speaker: Mr Kenichiro Nagayoshi (SRON Netherlands Institute for Space Research)
• 88
Development of a Wide-Range X-ray Emission Spectroscopy Measurement System with Transition Edge Sensors and Microwave Multiplexed Readout

High-resolution X-ray emission spectroscopy (XES) can offer element-specific insight into the oxidation state and chemical environment of a compound through energy shifts in emission peaks and their minor satellites. Compared to X-ray absorption spectroscopy, emission spectroscopy is less developed from both a theoretical and practical standpoint, and the ≲ 1 eV shifts demand detectors with high energy resolution and high efficiency. As part of the LANL Hyperspectral X-ray Imaging (HXI) project, we are commissioning a workstation for high-resolution X-ray emission spectroscopy of samples from 0.2 – 15 keV using transition edge sensors (TESes) to catalog the variation of peak and satellite shifts and develop accurate theoretical models applicable to XES. The TES detector array from NIST is installed in a High Precision Devices model 107 cryostat with 128-channel microwave multiplexed readout. The 240-pixel array is an equal mix of low- and high-dynamic range pixels to cover the full energy range to 15 keV, with 2 eV FWHM resolution at 1.25 keV on the low-range pixels and an expected 5 eV resolution at 6 keV for the high-range pixels. A mix of low- and high-range pixels may be bonded to the 128-channel readout. A UHV sample chamber attached to the bottom of the cryostat holds multiple sample stubs for X-ray excitation with either low- or high-energy X-ray generators (maximum emission of 15 keV and 50 keV respectively). The sample chamber vacuum is isolated from the cryostat vacuum by a LuxelHT window that (combined with three 100 nm-thick Al IR filters) gives 5.2% transmission at the 277 eV C K line. This system will allow the XES measurement of a wide range of transition metal and actinide samples with simultaneous access to multiple metal and ligand emission bands to support the analysis of HXI data from the future HXI project SEM/TES.

Speaker: Matthew Carpenter (Los Alamos National Laboratory)
• 89
Development of Gamma-Ray Position-Sensitive Transition-Edge Sensor Microcalorimeters

We are developing Position-Sensitive Transition-edge sensor (TES) microcalorimeters (PoSTs) to detect gamma-rays up to a few MeV. Each PoST consists of a long absorber with a TES on each end of the absorber and works as a one-dimensional imaging spectrometer. We fabricated PoSTs with 0.5 mm x 0.5 mm x 18.8 mm lead absorbers and TESs with transition temperature of 171 mK. We irradiated the devices with gamma rays from a Cs-137 source. Gamma-ray pulses of the PoSTs show a correlation between pulse height and rise time, whereas our single-pixel gamma-ray TES microcalorimeters show no such correlation. We divided the PoST pulses in the 662 keV line into 13 groups after sorting them by rise time to determine effective pixels. We compared average pulses of the 13 effective pixels to numerical simulation. The actual pulses and simulated pulses are in good agreement.

Speaker: Prof. Naoko Iyomoto (Kyushu University)
• 90
Development of Gamma-Ray Transition-Edge-Sensor Microcalorimeters on Thick Membranes

We are challenging to measure gamma rays in the high energy band of 200 keV-2 MeV.For this purpose, our gamma-ray transition-edge-sensor (TES) microcalorimeters have a large absorber (1mm×1mm×1mm). For mechanical robustness and fast decay time, the membrane of our gamma-ray TES microcalorimeters are made of silicon and at present ten times thicker than those of X-ray TES microcalorimeters. However, if the thermal conductance of the membrane is too high, thermal noise arising from Compton scattering on the silicon substrates degrades the energy resolution.
Therefore, it is necessary to select an appropriate thermal conductance of the membrane. We fabricated various TES microcalorimeters in which we changed the shape and the size of the membranes and measured the thermal conductance of them. Also, we are trying to reduce the influence of Compton scattering by reducing the volume of silicon substrate.

Speaker: Mr Tetsuya Tsuruta (Kyushu University)
• 91
Development of low threshold detectors for light dark matter detection

We developed a 5x5x5 mm3 crystal detector with an MMC readout. The detector was designed to achieve low energy threshold for direct detection of low mass dark matter. A pure CaF2 crystal was adopted as a target. This absorber crystal had a strong thermal contact to a metallic magnetic calorimeter (MMC) sensor via thin gold film evaporated on its surface. The MMC sensor and the gold film were directly bonded together using cold diffusion welding. We will present the result of the detector performance together with the detector model of the heat flow.

Speaker: Hyelim Kim
• 92
Development of Low-Frequency Space-Optimized TES Bolometer Arrays for LiteBIRD

LiteBIRD is a cosmic microwave background polarization experiment with the goal of measuring the tensor-to-scalar ratio with a total uncertainty of $\delta r$ < 0.001. It will survey the full sky for three years in 15 frequency bands spanning 34 to 448 GHz. We are developing detector arrays for the six lowest frequency bands, 34 to 99 GHz. The arrays are populated with lenslet-coupled sinuous antennas, two types of triplexer filters, and transition-edge sensor (TES) bolometers. We have measured the electrical and thermal properties of these space-optimized TES bolometers. The design balances requirements for low saturation power of the space environment while maintaining a fast time response for use with a continuously-rotating half-wave plate. We have achieved detector saturation powers below 1 pW, with time constants faster than 1 ms, at a 100 mK bath temperature using both time- and frequency-division multiplexed SQUID readout systems.

Speaker: Dr Greg Jaehnig (University of Colorado Boulder)
• 93
Development of metallic magnetic calorimeter arrays with embedded $^{163}$Ho for the ECHo experiment

The Electron Capture in $^{163}$Ho (ECHo) collaboration plans to reach sub-eV sensitivity level on the effective electron neutrino mass by the analysis of a high energy resolution and high statistics electron capture spectrum of $^{163}$Ho. Large arrays, of the order of 100 pixels each, of metallic magnetic calorimeters (MMCs) with enclosed $^{163}$Ho, read out utilizing microwave SQUID multiplexing, have been selected to achieve this goal. With first prototypes of MMCs having $^{163}$Ho ions implanted in their absorbers and operated at about 15 mK, energy resolutions $\Delta E_{\mathrm{FWHM}}$ below 5 eV were achieved. . We show results obtained in the characterization of an MMC array in terms of activity, energy resolution and intrinsic background of single pixels. We present the design of next generation MMC arrays for the ECHo experiment and discuss the processes to reliably embed high purity $^{163}$Ho source in detector absorbers. . In conclusion, we discuss how the production of MMC arrays, including micro-fabrication and 163Ho enclosing, can be scaled up to cope for the requirement of the up-coming phases of the ECHo experiment.

Speaker: Federica Mantegazzini (Kirchhoff Institute for Physics, Heidelberg University)
• 94
Development of Microwave Kinetic Inductance Detectors for near-IR single photon counting

We have developed Microwave Kinetic Inductance Detectors suitable for near-IR single photon counting. Our films are made of titanium and titanium nitride, deposited in a multi-layer structure Ti/TiN/Ti/TiN with a total thickness of 44 nm. The film has a transition temperature of 1.2 K and a surface kinetic inductance of 34 pH/sq. The resonator was designed with lumped elements and consists of two blocks of interdigitated capacitors connected by a meandered stripe inductor of 128 μm$^3$. The resonator resonance frequency is 6.8 GHz and the internal quality factor is 125000. We have estimated the kinetic inductance fraction α=0.86 .The detector is read out with the usual homodyne scheme and has been calibrated with light pulses produced by a laser diode with wavelength 1550 nm. We measure a FWHM energy resolution = 0.44 eV which is sufficient to resolve events with up to 4 photons and is within a factor of two from the best value published in literature. In the next design we aim at a further improvement by reducing the inductor volume by about a factor of 10.

Speaker: Dr Renato Mezzena (Dipartimento di Fisica, Università di Trento and INFN - TIFPA Trento)
• 95
Development of MMC based combined photon and phonon detector for rare event searches

In the search for rare events, a simultaneous measurement of photons and phonons produced after an event in a scintillating crystal operated at mK temperatures enables an efficient background rejection. This is due to the fact that the light yield depends on the mass, allowing for particle discrimination. This approach can be used for both neutrinoless double beta decay and dark matter searches. We present the design of a combined photon and phonon detector based on metallic magnetic calorimeters (MMCs). Simulations predict an energy resolution of $\Delta E_{\mathrm{FWHM}}\,<\,10\,$eV, a signal risetime of $\tau_0\,<\,50\,\mu$s and a signal decay time $\tau_1\,<\,10\,$ms for the photon detector and $\Delta E_{\mathrm{FWHM}}\,<\,100\,$eV, $\tau_0\,<\,200\,\mu$s and $\tau_1\,<\,10\,$ms for the phonon detector. The combined photon and phonon detector concept will be described with emphasis on the tower design of a multi-crystal setup. The challenges of the fabrication steps will be discussed. In addition, we will present the results of characterizations of first prototypes of such photon and phonon detectors.

Speaker: Andreas Fleischmann (Kirchhoff Institute for Physics, Heidelberg University)
• 96
Development of the low-frequency detectors for BICEP Array

The BICEP/Keck (BK) experiment aims to detect the imprint of primordial
gravitational waves in the Cosmic Microwave Background polarization,
which would be direct evidence of the inflation theory. While the
tensor-to-scalar ratio r has been constrained to be <0.06 at 95% c.l.,
further improvements on this upper limit are hindered by polarized
Galactic foreground emissions. The 30/40 GHz receiver of the BICEP Array
(BA), targeting to constrain the synchrotron foreground with
unprecedented accuracy within the BK sky patch, will be deployed at the
end of 2019. The receiver has a focal plane with 11 single-band detector
tiles and one dual-color tile with the newly designed broad-band planar
antenna. In this talk, I will show the full development path of the
30/40 GHz detectors from design to tests results. The low optical and
have low saturation power in order to be photon-noise dominated. To
achieve that, we have explored new leg designs for low island-to-bath
thermal conductivity (G). To boost detector fabrication throughput, we
have moved from 4" to 6" wafers, which introduced new challenges in the
fabrication process, such as thickness uniformity across the tile. I
will discuss how we overcame these issues and will present the measured
detector parameters (G, Tc, Psat etc.) and optical performance
(responsivity, beam, spectra). I will present on-sky noise performance
estimates based on the lab measurements and will discuss the sensitivity
forecast for the constraints on synchrotron amplitude and spectral
index.

Speaker: Ms Cheng Zhang (Caltech)
• 97
Development of Transition-Edge Sensor X-ray Microcalorimeter Linear Array for High Energy Applications

We are currently building a transition-edge sensor (TES) X-ray spectrometer for the Advanced Photon Source at Argonne National Laboratory for energies less than 20 keV in collaboration with National Institute of Standards and Technology (NIST). The spectrometer consists of application specific TES sensors for pilot X-ray emission spectroscopy (XES) and X-ray absorption fine structure (XAFS) experiments. We propose to develop and fabricate TES sensors for the very hard X-ray energy range (20-100 keV). We have recently published an article where we present a design optimization for a linear TES array for energy-dispersive X-ray diffraction (EDXRD) and Compton scattering measurements [1]. We present our progress on simulation results, preliminary sensor layouts, and proof-of-principle fabrication of millimeter long SiN membranes.

This work was supported by the Accelerator and Detector R&D program in Basic Energy Sciences’ Scientific User Facilities (SUF) Division at the Department of Energy. This research used resources of the Advanced Photon Source and Center for Nanoscale Materials, U.S. Department of Energy Office of Science User Facilities operated for the DOE Office of Science by the Argonne National Laboratory under Contract No. DE‑AC02‑06CH11357. This work made use of the Pritzker Nanofabrication Facility of the Institute for Molecular Engineering at the University of Chicago, which receives support from Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), a node of the National Science Foundation’s National Nanotechnology Coordinated Infrastructure.

[1] D. Yan et al; Modelling a Transition-Edge Sensor X-ray Microcalorimeter Linear Array for Compton Profile Measurements and Energy Dispersive Diffraction, arXiv:1902.10047 (2019).

Speaker: Umeshkumar Patel (Argonne National Laboratory)
• 98
Diamond cryogenic detector for low-mass Dark Matter searches

Despite the multiple and convincing evidences of the existence of Dark Matter (DM) in our Universe, its identification is one of the most pressing questions in particle physics. As of today there is no unambiguous hint which could clarify its particle nature. For these reasons, a huge experimental effort is ongoing, trying to realise experiments which can probe different DM properties. In particular, direct searches experiments are trying to cover the widest possible mass range, from a few MeV up to TeVs.
Particularly suited for sub-GeV sensitivity are detectors made of light nuclei, which are sensitive to the scattering-off of light DM candidates. Among them, carbon-based materials used as detection medium would be able to probe value of low-mass DM masses, down to the MeV range.
Thanks to their cryogenic properties (high Debye temperature and long-lived phonon modes), carbon-based materials operated as low temperature calorimeters could reach an energy threshold in the eV range, and would allow for the exploration of new parameters of the DM- nucleus cross section.
Despite several proposals, the possibility of operating a carbon-based cryogenic detector has not been demonstrated yet. In this contribution the preliminary results obtained with a diamond absorber operated with a TES temperature sensor will be reported. The potential of such a detector in the current landscape of dark matter searches will be also illustrated.

Speaker: Lucia Canonica
• 99
Diamond Detectors for Direct Detection of Sub-GeV Dark Matter

We propose to use high-purity lab-grown diamond for the detection of sub-GeV dark matter. Diamond targets can be sensitive to both nuclear and electron recoils from dark matter scattering in the MeV and above mass range, as well as to absorption processes of dark matter with masses between sub-eV to 10's of eV.
Compared to other proposed semiconducting targets such as germanium and silicon, diamond detectors can probe lower dark matter masses via nuclear recoils due to the lightness of the carbon nucleus. The expected reach for electron recoils is comparable to that of germanium and silicon, with the advantage that dark counts are expected to be under better control. Via absorption processes, unconstrained QCD axion parameter space can be successfully probed in diamond for masses of order 10 eV, further demonstrating the power of our approach.

Speaker: To Chin Yu (SLAC National Accelerator Laboratory)
• 100
Dynamic characterization of cryogenic optical photon detectors with Ir/Pt bilayer transition edge sensors

Low-temperature calorimeters (or phonon detectors) have proven to be great detectors to search for rare processes like neutrinoless double beta decay and dark matter interactions. While the massive calorimeters used in the aforementioned searches can achieve excellent energy resolution, their sensitivity is limited by the background radioactivity. One technique to enable event-by-event background rejection by reading out the phonon and photon signals simultaneously from a scintillating crystal or a Cherenkov light-emitting crystal. We have an ongoing R&D effort towards developing sensitive optical-photon detectors that can measure tiny amounts of scintillation/Cherenkov light from low-temperature calorimeters. The detectors use a novel Iridium/Platinum bilayer superconducting transition-edge-sensor (TES) that can be operated at temperatures ~ 30 mK. In this work we will show the characterization of optical photon detectors in terms of energy and timing resolution, together with a thermal model describing the steady state current-voltage characteristics and the dynamic response of the detector.

Speaker: Vivek Singh (University of California, Berkeley)
• 101
Expanding the Capability of Microwave Multiplexed Readout for Fast Signals in Microcalorimeters

Microwave multiplexing has become a key technology for reading out large arrays of x-ray and gamma ray microcalorimeters with mux factors of 100 or more. However, the desire for large mux factors and fast x-ray pulses for high photon counting rates drives system design towards high sensor current slew rate, which is typically handled by using a high sampling rate. Future experiments like the LCLS-II soft x-ray spectrometer and the LYNX x-ray microcalorimeter are expected to require sampling rates of 1 MHz or faster in order to meet count rate, mux factor, and x-ray energy range requirements.

In our microwave multiplexed readout scheme, the effective sampling rate is set by the frequency of the flux ramp modulation ($f_r$) used to linearize the SQUID response, and is generally limited to half the resonator bandwidth. The maximum current slew rate between samples is then nominally Φ$_0$$f_r/2M_{in} (where M_{in} is the input coupling) because it is generally not possible to distinguish phase shifts of >π from negative phase shifts of <-π. However, during a pulse, we know which direction the current ought to slew, and this makes it possible to reconstruct pulses where phase shifts are >π or even >2π. We show that if the slew rate on falling edge of the pulse is less than the nominal Φ_0$$f_r$/2M$_{in}$ limit, we can use a straightforward algorithm to identify and reconstruct pulses that exceed that limit on the rising edge. We demonstrate this on pulses produced by x-ray transition edge sensors, and find that the pulse reconstruction has minimal impact on energy resolution compared to arrival time effects induced by under-sampling the rising edge. If the rising edge is sufficiently sampled, this technique can increase the effective slew rate limit by more than a factor of two, thereby either reducing the bandwidth required or extending the energy range of measurable photons. The extra margin could also be used to improve crosstalk or decrease readout noise.

Speaker: Kelsey Morgan (University of Colorado Boulder)
• 102
Extending KIDs Optical Response to the Mid-IR for Future Space Observatories

The Galaxy Evolution Probe (GEP) is a concept for a NASA Astrophysics Probe-class space observatory to study the physical processes that have influenced galaxy evolution over cosmic time. This requires surveys of the mid- and far-infrared (IR) spectra of galaxies over a broad range of redshifts and cosmic environments. These mid and far-IR observations require large multi-frequency arrays of sensitive detectors. The GEP needs aluminum kinetic inductance detectors (KIDs) for wavelengths of 10-400 microns with NEPs on the order of 1x10$^{-18}$ W Hz$^{-1/2}$. We plan to use lens-coupled, aluminum lumped-element KIDs for the longer wavelengths, similar to those previously tested in our group. KIDs for wavelengths between 10 and 100 microns have not been implemented previously. We present an absorber design for KIDs sensitive to wavelengths of 10 microns shown to have approximately 75% absorption efficiency by HFSS simulations, challenges that come with optimizing our design to increase the wavelength range to 100 microns, and initial tests of our fabricated 10 micron KIDs.

Speaker: Joanna Perido
• 103
Fabrication of Bismuth Absorber Arrays for NTD-Ge Hard X-ray Microcalorimeters

The high spectral resolution detection of hard X-rays (E > 20 keV) is a challenging and nearly unexplored area in Space Astrophysics.
Traditionally used CdTe/CdZnTe semiconductor based hard x-ray detectors present moderate spectral resolution (several hundred eV @ 60 keV), while a resolution of few tens of eV could open new frontiers in the study of nuclear processes and high temperature plasma dynamics in energetic processes such as the coalescence of compact objects or energetic flares in the Sun or active stars. This can be achieved by using properly designed cryogenic microcalorimeters. Presently, such devices are currently investigated for the detection of soft X-rays from astrophysical sources (e.g. the TES microcalorimeters in the Athena X-ray Integral Field Unit instrument).
Within a research activity aimed at developing a NTD-Ge cryogenic microcalorimeter array detector for high resolution (about 50 eV @ 60 keV) detection of hard X rays (20 keV < E < 100 keV), we have set up an electroplating process to deposit high thickness (> 60 m) bismuth layers suitable for effective high energy photon absorption.
In this work we describe the fabrication of bismuth absorbers designed to be integrated on arrays of NTD-Ge sensors and discuss results from preliminary characterization.

Speaker: Dr Salvatore Ferruggia Bonura (Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Palermo, Palermo–Italy - Università degli Studi di Palermo, Dipartimento di Fisica e Chimica - Emilio Segrè, Palermo–Italy)
• 104
Fabrication of mushroom-type gold absorber for transition edge X-ray detectors

Absorber is a key element for superconducting transition edge X-ray detectors. We fabricated thick gold absorber with an overhanging structure. A Ti/Au seed layer was made by magnetron-sputtering deposition, and then several micrometers-thick gold absorber was made by electroplating. The resistivity of the gold absorber was determined from four-terminal measurements. The absorber was integrated with a transition edge detector. The heat capacity of the absorber was evaluated from the measurements of the effective time constant of the TES detector.

Speaker: Prof. Bo Gao (Shanghai institute of microsystem and information technology, Chinese Academy of Sciences)
• 105
Fabrication of Planar Integrated SIS Mixer Circuit with High Uniformity and High Yield

We have been developing Superconductor-Insulator-Superconductor (SIS) mixer integrated circuits (ICs) for highly compact multi-beam heterodyne receivers. The distinctive feature of the SIS mixer ICs is the incorporation of membrane-supported waveguide probes for signal and local oscillator coupling. This idea makes it possible to compactly accommodate many pixels on the focal plane and to broaden the field of view of mm/sub-mm wave radio telescopes.
The SIS mixer IC on a silicon-based chip in this study have a much larger area than a conventional SIS mixer on a glass chip. It is because the IC contains many planar circuit RF components which are implemented with metal waveguide structures in a conventional mixer. In this study, the area of the single pixel prototype IC chip we have designed is about 45 times larger than that of the conventional mixer chip at 2 mm wave length that has been developed before in our lab. The area of the IC chip will become even larger if multiple pixels are incorporated. In consequence, the on-wafer uniformity of circuit geometries and the SIS junction yield turn out to be essential.
We have been carrying out fabrication of prototype SIS mixer ICs with applying machine-aligned via-hole etching process together with insulator layer deposition with plasma enhanced chemical vapor deposition. This approach shows much improved circuit uniformity and SIS junction yield in comparison with the self-aligned lift-off process together with RF-sputtering of the insulator layers. In this presentation, we will report the fabrication processes and the characteristics of the prototype SIS ICs.

Speaker: Dr Shohei Ezaki (National Astronomical Observatory of Japan)
• 106
Fast readout cryogenic electronics for SIS photon detectors

Photon counting detectors for terahertz frequencies will open new frontiers in terahertz astronomy by measuring photon statistics and applying to intensity interferometry. To count large number of terahertz photons, we work on SIS (or STJ) photon detectors. In this presentation we discuss the readout cryogenic electronics with GHz bandwidth made of semiconductor circuits for the SIS photon detectors.
Single terahertz photon creates single quasi-particle current through SIS junction by photon assisted tunneling. We have successfully developed an SIS junction with low leakage current in the order of pA. The photo-voltage of the SIS junction is to be read out by cryogenic FETs with low gate leakage and capacitance. We selected two types of Gallium Arsenide FETs with junction gates (GaAs-JFET and Junction pHEMT) for this purpose. We have evaluated both types of FETs with various gate sizes at cryogenic temperature of 4 K, most of which show good I-V characteristics without anomalies such as kink or hysteresis. Typical drain current at 4 K is about half compared to that at 300 K. Gate leakage of GaAs-JFET was confirmed to be lower than fA, and Junction pHEMT is now under evaluation.
We plan to use two source followers in series, one at 0.8 K and another at 4 K, in order to decrease the output impedance down to 50 ohm to feed to the SiGe low noise amplifier. To detect a single terahertz photon, the FETs need to exhibit low gate capacitance of the order of fF to obtain signal significantly above the FETs' voltage noise. The gate capacitance of the FETs are also to be evaluated. We will present the measured performance of the FETs and discuss the prospects of terahertz photon counting.

Speaker: Hiroshi Matsuo (National Astronomical Observatory of Japan)
• 107
Flat low-loss silicon gradient index lens for millimeter and submillimeter wavelengths

Many applications in astronomy from tens of GHz to THz frequencies, such as CMB polarization studies and Sunyaev-Zeldovich effect observations, would benefit from low loss and wide bandwidth optics. Silicon is an excellent material for optics within this frequency range because of its high refractive index, achromaticity, lack of birefringence, low loss, high thermal conductivity, and strength.

Silicon’s high index, however, presents a challenge for antireflection (AR) treatment, which our approach addresses. Its two core elements are: 1) fabrication of multi-layer AR structures via multi-depth deep reactive ion etching (DRIE) and wafer-bonding; and 2) assembly of gradient index (GRIN) optics, flat-faced to be consistent with AR treatment, by bonding multiple silicon wafers patterned with the desired radial index profile by DRIE. Both the AR structures and the GRIN structures are made of sub-wavelength features (posts or holes) that change the effective refractive index of silicon. For AR structures, each AR layer has a different homogeneous index while for GRIN lenses, the index varies radially (higher in the middle and lower near the edge of a focusing lens). Moreover, GRIN lens design only uses holes so it can be physically continuous and thus edge-mountable. To reach the desired GRIN lens thickness, several identical etched wafers must be bonded together because we cannot use DRIE to etch vertical holes deeper than a few hundreds of µm with a high aspect ratio (up to approximately 20:1).

We present our results to date, which include the design, simulation, fabrication and measurement of a 100 mm diameter flat GRIN lens made of high resistivity silicon, combined with single- or double-layer AR structures, centered on 250 GHz.

Speaker: Dr Fabien Defrance (California Institute of Technology)
• 108
Full-Array Noise Performance of Deployment-Grade SuperSpec mm-wave On-Chip Spectrometers

SuperSpec is an on-chip filter-bank spectrometer designed for wideband moderate-resolution spectroscopy at millimeter and submillimeter wavelengths, employing TiN kinetic inductance detectors. SuperSpec technology will enable integral-field-unit spectrometers suitable for high-redshift line intensity mapping or multi-object spectrographs. We plan to deploy a demonstration instrument to the Large Millimeter Telescope (LMT) in mid-2019, featuring six independent single-polarization SuperSpec chips and covering 190-310 GHz with 100 channels each.

In previous results, we have demonstrated noise performance for individual detectors suitable for photon noise limited observations at excellent mm-wave observing sites. In these proceedings, we present the complete system-level noise performance of deployment-grade devices that we will use at the LMT, measured through a ROACH-based readout system. Array statistics such as NEP, responsivity, and low-frequency noise performance will be shown for all channels and compared to the expected observing conditions and planned scan strategy at the LMT.

Speaker: Dr Kirit Karkare (University of Chicago)
• 109
Gradient-index Silicon Optics for Millimeter-wave detectors

For quasi-optical elements in the millimeter and sub- millimeter range, silicon is an interesting material. Its high refractive index facilitates the production of compact and lightweight elements. Moreover, its thermal conductivity allows better thermalisation at cryogenic temperatures, and the loss tangent of bulk high-resistivity silicon (tan δ < 10- 4) is without competition.

Silicon is however very difficult to machine, and the high refractive index necessitates the use of anti-reflection coatings. Micromachined anti-reflection coatings have been developed for planar substrates but become increasingly more difficult for curved surfaces of e.g. lenses.

In this work, we follow a different approach. We use the fact that it is possible to modulate the refractive index of a material by inserting sub-wavelength voids and changing the fill factor of the voids. This way, a silicon metamaterial with a dielectric constant between 3.3 and 11.7 can be generated.

We describe our efforts to generate optical elements from thus modulated silicon, in particular the characterisation of a planar silicon lens with integrated anti-reflection coating. The presented technology offers great perspective in terms of compact, planar, low-loss optics. Moreover, the technology can be easily integrated with silicon detector wafers, and future developments that involve more elaborate anti-reflection coatings, integrated filtering, or microlens arrays, are just part of the possibilities.

Speaker: Dr Eduard Driessen (Institut de Radioastronomie Millimétrique)
• 110
HeRALD, a new detector concept for light dark matter direct detection

We present HeRALD (Helium Roton Apparatus for Light Dark matter), a new detector concept using superfluid helium as the target material for sub GeV dark matter nuclear recoil. Helium, in its superfluid state, promises a good kinematic matching to low mass dark matter with several channels for reading out nuclear recoils. The main idea of this detector design is that superfluid helium allows long-range ballistic propagation of phonon and roton excitions which, at the liquid-vacuum interface, can produce quantum evaporated single 4He atoms then sensed via their adsorption energy onto large-area low-threshold calorimetery. I will describe the R&D of this technique and I will discuss its capability of reaching recoil energy thresholds below 10 eV along with the sensitivity projections for a small scale detector (~1Kg) and its possibility of exploring new parameter space.

Speaker: Alessandro Serafin (University of Massachusetts (Amherst))
• 111
High energy background event identification using local group trigger in a 240-pixel X-ray TES array

A novel triggering function developed for 240 pixel Transition-Edge Sensors is demonstrated under the high rate of particle background. The function is integrated into the standard data acquisition system in the NIST TES framework. It enables any type of combination of trigger pattern when a pixel is triggered, which is called group trigger''. As a practical implementation, the primary trigger is distributed to the four physically nearest pixels. The group trigger function was utilized throughout the entire one-month J-PARC experiment for the measurement of the Kaonic-atom X-rays. This trigger allowed us to confirm that the increased background and degraded energy resolution we observed when operating the TES array in the presence of an ion beam are the result of thermal crosstalk from charged particles. We show that the maximum of the peak values among the four neighboring pixels is useful event selection parameter. We use cuts based on this parameter to improve the peak-to-background level in a measured x-ray energy spectrum by a factor of 2.5, while keeping 95¥% of measured events. This flexible group triggering technique allows us to improve the signal to noise on the very faint Kaonic Helium x-ray lines we are measuring, better understand our experiment environment, and we believe this technique may prove useful in other ground and space based TES applications.

Speaker: Dr Shinya Yamada (Tokyo Metropolitan university)
• 112
High impedance NbSi TES for very large arrays in X-Ray astronomy.

Large spectro-imagers for X-ray astronomy are highly needed. Consisting in micro-calorimeter arrays, technologies used for thermometers are based either on superconductor (TES) or metal-insulator (MIS, or Si-doped sensors) transitions. MIS are a good choice for their easy operability with classical electronics. TES allow high sensibilities detectors for the price of a complex multiplexing readout.
CSNSM (Orsay, France) has developed high impedance TES in NbSi. They combine the advantage of a great sensibility with a high impedance adapted to the standard microelectronics that facilitate the readout of very large matrices. Unfortunately, they suffer of an electron-phonon decoupling that induces a signal loss with classical readout schematics because the electrical signal depends on the electron temperature, while the incident photons modifies the phonon temperature.
Our experimental results with a new readout schematic demonstrate that phonons and electrons remain coupled, with the additional advantages of a great widening of the acceptable energy range without loss of sensibility, a complete stabilization of the thermal operating point, and the ability to set it arbitrarily according to optimization criteria.
This new schematic uses an active electro-thermal feedback : a heating device thermally coupled to the sensor sets the pixel temperature. When photon heat up the pixel, heating decreases in proportion so that pixel temperature remains almost constant. Measured quantity is no more the pixel temperature change, but the change of the heat dissipated by the heating.
Numerous tests on suspended pixels have been performed at 100 mK, proving the concept. A cobalt 57 source produces the signal. Experimental results and electro-thermal simulations are crosschecked. We developed an analytical model, based on block diagram analysis, to explain every parameter’s influence. It shows that high resistivity TES are good candidates for very high sensibility spectro-imagers.

Speaker: Mr Galahad Jego (CEA - Saclay)
• 113
High resolution digitization system for the CROSS experiment

The signal digitization for CROSS, a bolometric experiment searching for neutrinoless double beta decay at LSC (Canfranc Underground Laboratory), will be based on a custom solution comprised of an analog-to-digital board interfaced to an Altera Cyclone V FPGA module. Each analog-to-digital board hosts 12 channels that allow data digitization up to 25 ksps per channel and an effective resolution of 21 bits at the typical sample rate required by the experiment (5 ksps). The board also allows to digitally select the cut-off frequency of the anti-aliasing filter with 10 bits of resolution from 24 Hz up to 2.5 kHz, as required by pulse-shape discrimination and fast scintillating bolometers. The FPGA is responsible for the synchronization of the analog-to-digital boards and for the data transfer to the storage, using UDP protocol on a standard Ethernet interface. Each FPGA can manage the data coming from 8 boards (96 channels), allowing an excellent scalability. In this contribution we will present a complete overview of the system, a detailed characterization of the system performance, and the results of the first tests with prototypes of the CROSS experiment.

Speaker: Paolo Carniti (MIB)
• 114
Holographic Beam Maps with Transition Edge Sensors

In this proceeding we will describe the effort made in our group to address the problem of the beam characterization of a small aperture telescope with wide field of view in the microwave band between 90 and 300GHz. We will describe the case of Transition Edge Sensors (TES), baseline choice for upcoming ground Cosmic Microwave Background (CMB) experiments such as the Small Aperture Telescope (SMA) for CMB-S4 or balloon borne experiments like the SPIDER polarimeter.
For those telescopes design the far field characterization of the beam is often impractical: the far field could be located kilometers away from the telescope’s aperture, and it is not unusual that such observatories are in remote and inaccessible sites like the Atacama Desert in Chile or the South Pole. The measure of the far field of a balloon borne experiment could be impossible because of mechanical reason, since they have limited pointing capabilities.
For this reason, the development of a robust and reliable technique to reconstruct the far field beam from holographic measures of the near field beam is necessary.
What makes the effort described in this work unique is twofold: because of the frequency range under study the precision of the positioning of the scanning probe needs to be a fraction of the corresponding wavelength of the radiation, requiring a large micrometric scanning stage; secondly the TES detectors have a typical time constant of about few milliseconds, this means that the radiation is able to travel several wavelength in one time constant making a direct phase measure very challenging.
To overcome those difficulties, we designed a custom automated frame to hold and move the probes with the required accuracy. The probe signal is generated by mixing two slightly offset monochromatic sources so that their intermediate frequency (IF), falls in the detector’s band. The detector’s response is then modulated at the same IF.

Speaker: Dr Riccardo Gualtieri (University of Illinois at Urbana Champaign)
• 115
HUBS: Hot Universe Baryon Surveyor

In China, HUBS is being proposed as a major X-ray mission for the next decade. It is designed to effectively probe hot gas in the circumgalactic and intergalactic space and thus to address the long-standing issue of "missing" baryons in the local universe. The hot gas is expected to produce only weak emission in soft X-rays, due to its low density, making it technically difficult to detect. On the other hand, the spectrum of the emission is expected to be line rich, so it would be quite effective to detect the gas in relatively bright lines. The scientific objective of HUBS is not just to find the "missing" baryons, but to see their spatial distribution and to measure their physical and chemical properties. An instrument with a combination of high spectral resolution, large effective area, and large field of view would be required for such purposes. HUBS will couple a large TES-based X-ray imaging array to an X-ray telescope, to satisfy these requirements. A preliminary design of HUBS will be presented.

Speaker: Dr Wei Cui (Tsinghua University)
• 116
Improving detection efficiency using polycapillary optics for broadband, ultrahigh resolution spectroscopy of particle induced X-rays with TES microcalorimeter arrays

We discuss the improvements in wide energy range, energy dispersive X-ray emission spectroscopy in the particle induced mode (PIXE) achieved by optical focusing of X-rays to high-energy resolution superconducting transition-edge sensor arrays. TES-PIXE technique offers great energy resolution for multi-element samples consisting of even hundreds of X-ray peaks with nearly overlapping energies [1]. TES-PIXE can provide orders of magnitude better detection limits and energy resolution compared to the traditional silicon drift detector (SDD), which gives the possibility to probe trace impurities within samples [2]. Here, we discuss recent progress in performing TES-PIXE spectroscopy in air, by using a polycapillary lens and an external ion beam. Such an external beam PIXE is a non-destructive technique, which can be used to measure precious museum artefacts and delicate samples that cannot go into a vacuum chamber. The use of the polycapillary lens increases the effective solid angle of the detector, increasing the number of X-rays detected up to a factor of three in the 0.5-5.5 keV energy range [3]. The polycapillary lens also removes the need for additional proton filters, enabling detection of lighter elements, down to oxygen.

[1] M. R. J. Palosaari, M. Käyhkö, K. M. Kinnunen, M. Laitinen, J. Julin, J. Malm, T. Sajavaara, W. B. Doriese, J. Fowler, C. Reintsema, D. Swetz, D. Schmidt, J. N. Ullom, and I. J. Maasilta, Phys. Rev. Applied 6, 024002 (2016)
[2] M. Käyhkö, M.R.J. Palosaari, M. Laitinen, K. Arstila, I.J. Maasilta, J.W. Fowler, W.B. Doriese, J.N. Ullom, T. Sajavaara, Nucl. Instrum. Methods Phys. Res. B 406, 103 (2017)
[3] M. Käyhkö, M. Laitinen, K. Arstila, I.J. Maasilta, T. Sajavaara, Nucl. Instrum. Methods Phys. Res. B 447,59-67 (2019)

Speaker: Mr Ari Helenius (University of Jyväskylä)
• 117
Increased multiplexing of superconducting microresonator arrays by post-characterization adaptation of the on-chip capacitors

We present an interdigitated capacitor trimming technique for fine-tuning the resonance frequency of superconducting microresonators and increasing the multiplexing factor. We first measure the optical response of the array with a beam mapping system to link all resonances to their physical resonators. Then a new set of resonance frequencies with uniform spacing and higher multiplexing factor is designed. We use simulations to deduce the lengths that we should trim from the capacitor fingers in order to shift the resonances to the desired frequencies. The sample is then modified using contact lithography and re-measured using the same setup. We demonstrate this technique on a 112-pixel aluminum lumped-element kinetic-inductance detector array for 1mm band. Before trimming, the resonance frequency deviation of this array is investigated. The variation of the inductor width plays the main role for the deviation. After trimming, the mean fractional frequency error for identified resonators is -6.4e-4, with a standard deviation of 1.8e-4. The final optical yield is increased from 70.5% to 96.7% with no observable crosstalk beyond -15 dB during mapping. This technique could be applied to other photon-sensitive superconducting microresonator arrays for increasing the yield and multiplexing factor.

Speaker: Shibo Shu (Institut de Radioastronomie Millimétrique)
• 118
Ka band narrowband parametric amplification via non-linear dynamics in superconducting waveguide cavities

Narrowband parametric amplifiers with superconducting (SC) thin films on planar transmission lines have been realised by numerous groups. These paramps rely on resonators with non-linear elements within them to allow for harmonic generation that gives rise to signal gain when certain conditions are satisfied. Such params, however, have not yet been realised in SC circular and rectangular waveguide resonators. Considering very small frequency scales of the order of 10-100s of kHz where the dispersion in waveguides is effectively small – the phase matching condition which is key to parametric gain may also be satisfied. Hence, narrowband gain within the profile of a resonance of a cavity resonator is possible.

Reported here are the results from the investigations of SC resonators realised with circular and rectangular waveguides in series and parallel arrangements to the waveguide feedline. These waveguide cavities – milled from bulk Nb or copper with a thin layer of Nb deposited via chemical vapour deposition (CVD) – were designed such that their resonance frequencies lay within Ka band (26.5 – 40 GHz). This frequency range was chosen to accommodate for an in-house-built test cryostat with Ka band thermal breaks that ensured thermal isolation of the waveguide cavities and allowed temperatures below 1 K to be reached. Characterisation of the transmission properties of the cavities showed temperature and power dependant behaviour and the appearance of inherently non-linear duffing oscillator features – analogous to weak link non-linearities in SC planar transmission lines – manifesting themselves as ‘kinks’ of the order of a few kHz in the S-parameter spectra of the resonances. Harmonic generation, as a result of non-linear phenomena, was observed when two separate tones were injected into the cavities. Under certain frequency (and phase) conditions this harmonic generation led to parametric amplification of a weak signal in the presence of a strong pump.

Speaker: Mr Danielius Banys (The University of Manchester)
• 119
KATANA – Koolstof (Carbon) Atom Tomography with Advanced Nanotechnology for Astronomy

Intensive submm-wave continuum imaging of the sky has discovered several high-redshift ultra-luminous infrared galaxies (ULIRGs), and follow up spectroscopic measurements have partially resolved their redshift distribution. But much of the dust-obscured galaxy formation in the early universe is traced by much less bright infrared galaxies, which are hard to detect using classical imaging systems. KATANA (Koolstof (Carbon) Atom Tomography with Advanced Nanotechnology for Astronomy) is designed to detect ~100 times more dusty galaxies ever found by measuring their redshift and spatial distribution at once.

KATANA is a 147-pixel imaging spectrometer covering 3×20 GHz of bandwidth around 270 GHz, 340 GHz and 400 GHz with a frequency resolution (R=F/dF) of 500. The bandwidth corresponds to sliced redshift ranges of 5.9-6.4, 4.3-4.7, and 3.6-3.8 for the [CII] line. The key technologies of KATANA are: a dual-polarization sensitive broadband antenna, an on-chip planar filter-bank spectrometer, and NbTiN-Al hybrid MKIDs (Microwave Kinetic Inductance Detectors) to readout the spectral channels. It requires 24,000 MKIDs to fully cover the target bandwidth with 147 spatial pixels. Those technologies are currently being developed at SRON/TU Delft for the DESHIMA and MOSAIC projects.

We carried out sensitivity calculation of a [CII] line emitter search with KATANA on the ASTE and APEX telescopes. We also calculated the sensitivity on the LMT and IRAM 30m telescope with a different band configuration of 220 GHz, 270 GHz, and 340 GHz. Combination of its simultaneous broad bandwidth and large number of pixel enables us to explore an unprecedented volume of the universe that even ALMA cannot cover. KATANA has great potential to cut a new window open for studying dust-obscured formation of massive galaxies by even revealing the abundance of high-z luminous infrared galaxies (LIRGs) that have never been found so far by any submm-wave continuum surveys due to their confusion limits.

Speaker: Kenichi Karatsu (SRON/TU Delft)
• 120
Large Area TES Chip with 40meV Resolution

Future low mass Dark Matter searches will require sensitivity to single optical phonons, corresponding to thresholds of about 100meV. This motivates the design of sensors with relatively large areas, and excellent energy resolution.

In this talk I will discuss the performance of a $100\mu\mathrm{m}\times 400\mu\mathrm{m}$ Tungsten Transition Edge Sensor (TES) with a $T_c$ of 40mK. This device has a measured Noise eqivalent power (NEP) of $1.5\times 10^{-18}\mathrm{W}/\sqrt{\mathrm{Hz}}$, and a bandwidth of $2.6$kHz, suggesting a resolution of a dirac delta energy deposit of 40meV. This energy resolution is comparable to world leading Microwave Kinetic Inductance Detectors (MKIDs) and TES based optical photon sensors, but with a device of much larger size.

Speaker: Mr Caleb Fink (University of California Berkeley)
• 121
Low temperature measurement on directional dependence of phonon-scintillation signals from a zinc tungstate crystal

In dark matter direct-detection experiments, the detection limits of most detectors are confined with the backgrounds originating from coherent neutrino-nucleus scattering. One of the possible methods to break the neutrino background floor is a use of the directional dependence of detector response. We employed ZnWO4 crystals as an anisotropic target material for the simultaneous detection of phonon and scintillation signals based on MMC readouts. The crystal is known to have birefringence properties depending on its crystal axes. Its low-temperature properties are well suited for phonon-scintillation detection. Here we report on the recent progress in low-temperature measurement using a ZnWO4 crystal that demonstrated clear dependence of scintillation signals on different incident directions of alpha particles relative to the crystal axes. We found the signal amplitudes were differed by 13.2 % in the light channels. However, the high energy resolution in the heat channels showed no measureable difference within 0.07 %. We will discuss the crystal properties and features for the directional WIMP detection.

Speaker: Dr JA Jeon (Center for Underground Physics, Institute for Basic Science)
• 122
Low Temperature MMC Detector Arrays for the IAXO experiment

The International Axion Observatory (IAXO) is searching for axions or axion-like particles generated in the Sun. A large magnetic field is used to convert solar axions to photons via the Primakoff effect. The major part of the expected spectrum considering only axion-photon coupling covers an energy range up to 10 keV with its maximum at about 3 keV. X-ray detectors with high efficiency in this energy range and low intrinsic background are required. Low temperature metallic magnetic calorimeters (MMCs) fulfil these requirements and can reach very low thresholds below 100 eV. We present the design of a new detector system for the IAXO experiment with the possibility to operate two different kinds of two dimensional MMC arrays. The setup is designed to host a large area MMC array with moderate energy resolution aiming to discover events related to axions. If axions were discovered the focus would move to spectroscopic studies. In this case a smaller MMC array featuring higher energy resolution would replace the initial array using the same setup. We show the current status of the experimental platform and discuss methods to identify background events based on pulse shape analysis and events coincidence in several pixels.

Speaker: Loredana gastaldo (Kirchhoff Institute for Physics, Heidelberg University)
• 123
Low-loss Microstrip Transmission Line Fabricated with Improved Liftoff Process

The µ-Spec integrated spectrometer operating at ~500 GHz, employs thin film superconducting Nb microstrip transmission lines deposited directly on a thin (450 nm) single-crystal silicon dielectric. This single-crystal silicon layer is chosen as the dielectric layer due to its low intrinsic loss, with the goal of achieving both high-efficiency and precise phase control in a compact spectrometer architecture. To avoid roughening or etching through the thin single-crystal silicon dielectric a liftoff technique was developed for patterning these microstrip transmission lines and ground plane structures. This two-layer liftoff process was designed for use with sputter deposition and resulted in a US patent. Although this original technique provided precise control of linewidth, results of initial prototype spectrometer devices and separate diagnostic co-planer waveguide resonator devices showed that unexpected loss was being introduced due to the lift-off process. This extra loss was believed to be due to the “tails” (thin tapered regions) at the edge of the metal traces resulting from the sputtering process, as well as an amorphous oxide layer at the Nb-Si interface. We have since demonstrated an improved lift-off technique, which provides a clean metal-Si interface and removes the loss-inducing tails by a two-step selective etching method. This results in a decrease in microwave loss by more than an order of magnitude when measured in co-planar waveguide microwave resonator structures. We present these microwave test results and also SEM and TEM images of the microstrip interfaces and edge profiles before and after application of the improved process.

Speakers: Larry A. Hess (NASA Goddard Space Flight Center) , Dr Larry Hess (NASA Goddard Space Flight Center) , Larry Hess (NASA\Goddard Space Flight Center)
• 124
Lowering the energy thresholds for the CUORE Experiment: A comparison between Optimum Trigger and Derivative Trigger Algorithm performances

CUORE (Cryogenic Underground Observatory for Rare Events) is a tonne-scale cryogenic detector located at the Laboratori Nazionali del Gran Sasso exploiting bolometric technique to search for neutrinoless double beta decay of 130Te. The experimental signature is a sharp peak at the Q value of the decay in the summed energy spectrum of the electrons emitted.
Thanks to its very low background and large source mass, CUORE is also a powerful tool to study a broad class of low energy phenomena such as solar axions or WIMP scattering. However, the possibility to conduct such sensitive searches strongly depends on the energy threshold.
Moreover, as we expect a neutrinoless double beta decay to be fully contained in one crystal, we exclude from the final energy spectrum decays depositing energy in multiple crystals within a certain coincidence window.
The trigger configuration influences the anti-coincidence selection in two ways: the timestamp assigned to physical events and above all the energy threshold for coincident events.

First CUORE data were acquired with the derivative trigger algorithm, with energy thresholds ranging from 20 to 100 keV. However, another trigger algorithm based on the optimal filter technique has been developed in these years. Data are filtered in the frequency domain in order to maximise the SNR. As a result, the noise superimposed on physical events is strongly reduced and the energy thresholds can be lowered. Currently CUORE data are re-triggered exploiting this technique.

In this contribution we will present a comparison of the performances of the two trigger methods in the analysis steps for the search of neutrinoless double beta decay of 130 Te, with particular attention to the improvement obtained with the optimum trigger in the background reduction with anti-coincidence selection.

Speaker: Mrs Alice Campani (Università degli studi di Genova, INFN )
• 125
Measuring Transmission Line Losses at sub-mm wavelengths with an on-chip Fabry-Perot resonator

Transmission line losses at sub-mm wavelengths present a significant challenge for highly integrated superconducting circuits, such as on-chip spectrometers, multi-color/dual polarization detectors for measurements of the CMB or phased array antennas. In the case of on-chip spectrometers like DESHIMA or SuperSpec, an internal loss better than $\tan^{-1}\delta = Qi \sim 10^4$ is required to eliminate power loss at both the individual filters and on the path between the antenna feed and the filterbank. While ohmic losses are negligible at frequencies significantly below the gap frequency of the superconductor ($2\Delta \approx1.1\$THz for NbTiN), other loss mechanisms become significant, such as radiation loss in the case of co-planar waveguides (CPW) and dielectric loss in microstrips (MS). At very high frequencies, above $500\$GHz for NbTiN, also the superconducting losses can increase.

We present the design and measurement results for a novel lab on-chip experiment capable of characterizing the internal losses of arbitrary transmission line geometries at frequencies up to 1 THz allowing accurate loss tangent estimates down to $\tan\delta =10^{-4}$. We use a Fabry-Perot resonator operated at mode numbers $n > 50$ that is coupled to a frequency-tunable THz source via a lens-antenna. The power transmitted through the Fabry-Perot is read out using an Al-NbTiN hybrid CPW microwave kinetic inductance detector(mKID). Multiple chips with both CPW and MS transmission lines have been designed, fabricated and measured using NbTiN as a lossless superconductor and a-Si as dielectric in case of the microstrips. Measurements were carried out in a $^3$He/$^4$He sorption cooler at $250\$mK at frequencies from 320 to 370 GHz.
We find $Q_i> 1.5\times10^4$ for CPW resonators and $Q_i = 1\times10^4$ for PECVD deposited a-SI, reaching the performance required for the implementation of microstrip filters in on-chip spectrometers.

Speaker: Sebastian Hähnle (SRON, Netherlands Institute for Space Research)
• 126
MetroMMC: Electron-capture spectrometry with cryogenic calorimeters for science and technology

Accurate decay data on radioactive nuclides are necessary for many fields of science and technology, ranging from medicine and particle physics to metrology. However, data that are in use today are mostly based on measurements or theoretical calculations that are rather old. Recent measurements with cryogenic detectors and other methods show in some cases significant discrepancies to both older experimental data and theory. Moreover, the old results often suffered from large uncertainties. This is true especially for electron-capture (EC) decays, where only a few selected radionuclides were measured at all.
To systematically address these shortcomings, the European metrology project MetroMMC aims at investigating 6 radionuclides decaying by electron capture. The nuclides are chosen to cover a wide range of atomic charges Z, which results in a wide range of decay energies and includes different decay modes, such as pure EC or EC accompanied by γ- and/or β+-transitions.
Metallic magnetic calorimeters (MMCs) are cryogenic energy-dispersive detectors with high energy resolution and low energy threshold, that are well suited for total decay energy and X-ray spectrometry. Within the MetroMMC project, these detectors are used to apply calorimetry with highest energy resolution to obtain X-ray spectra of external sources as well as fractional EC probabilities of sources embedded in a 4$\pi$ absorber. Experimentally determined nuclear and atomic data are then compared to newly developed state-of-the-art theoretical calculations which are also being developed within the project.
This contribution will introduce the MetroMMC project and in particular its experimental approach. The challenges in EC spectrometry are to adapt the detectors and the source preparation to the different decay channels and the wide energy range involved, while keeping the good resolution and especially the low energy threshold to measure the captures from outer shells.

Speaker: Philipp Chung-On Ranitzsch (PTB Braunschweig)
• 127
Microcalorimetry of carbon ion beam for medical treatment by transition edge sensor

Heavy ion beam is used in radiotherapy for cancer. Unlike in other radiation therapies, direct ionization plays a large roll in heavy ion therapy. It is considered that the secondary electrons emitted in the minute area around the track of a heavy ion beam plays a roll in the direct ionization, which has not been quantitatively evaluated yet. In order to ultimately detect the energy transfer in this minute region (microdosimetry), a detector which has a greater energy resolution than conservative detectors is needed. In this report, we precisely measured the energy of each carbon ion in carbon ion beam for treatment using a transition edge sensor (TES).
Carbon ion beam of 100MeV/u which was irradiated by Heavy Ion Medical Accelerator in Chiba (HIMAC). The TES we used in this experiment is made of bilayer of Ir and Au, and a Sn absorber was connected to the bilayer.
In order to measure the energy of carbon ion beam where the beam is around the Bragg peak, attenuators made of Al was set between the beam port and the TES. The energy of the beam was so large that the absorber was saturating during events. Since there is a correlation between saturation time and the energy of the heavy ion, we decided to collect the length of saturation time for events and made a histogram. We changed the thickness of the attenuator and made histograms for each thickness. As the thickness of the attenuator increases, the saturation time which showed the peak of each histogram increased. This matches the Bragg Curve of carbon ion beam. In addition, it appears that the variation of the histogram increased, as the thickness of the attenuator increased. It is assumed that the TES was able to read out the variation of the physical events that occurs when a carbon ion goes through the attenuator.
We have succeeded in measuring the energy of each carbon ion in the carbon ion beam. This may contribute to the establishment of a new method of dosimetry of carbon ion beam for treatment.

Speaker: Ryan Smith (University of Tokyo)
• 128
Microfabrication of TES microcalorimeters for the HOLMES experiment

HOLMES is an experiment aiming at pushing down the sensitivity on the smallest neutrino mass at the order of ∼ eV performing a calorimetric measurement of the Electron Capture decay spectrum of 163Ho. For reaching its goal, HOLMES will deploy an array of 1000 microcalorimeters based on Transition Edge Sensors with gold absorbers in which the 163Ho will be ion implanted. A major challenge is represented by the fabrication of the microcalorimeters with the required amount of 163Ho (300 Hz/det). Therefore, the fabrication process needs to be compatible with ion implantation without impairing the detector performances. The gold absorber will be fabricated in more steps: before, during and after the ion implantation. In particular, the gold deposition during the embedding process is intended to compensate for the absorber atom sputtering caused by ion implantation and to control the 163 Ho concentration in the detectors. The implanted area will finally be encapsulated in-situ to ensure the fully containment of the decay energy and to avoid oxidation of the holmium.
We describe here the multi-step microfabrication process, mainly focusing on the last steps.

Speakers: Mrs Elena Ferri, Flavio Gatti (GE)
• 129
Microwave SQUID multiplexer for readout of optical TES array

Optical Transition Edge Sensor (TES) detectors are highly desirable for two-dimensional single-photon multi-color imaging, especially in biology. Recently, we have demonstrated the single photon spectroscopic imaging with an optical TES [1]. It takes 20 to 40 minutes to obtain an image. To decrease the measurement time, multi-pixel detectors are necessary. A Microwave SQUID Multiplexer (MW-Mux) [2] which consists of superconducting resonators and rf-SQUID is a powerful device for readout of the optical TES array.
In previous work, we successfully measured output signals of an optical TES with MW-Mux. Fig. 1 shows the energy spectrum of faint light source with a wavelength of 1550 nm. The observed energy resolution of 0.42 eV for the single photon peak (= 0.8 eV) was worse than that measured with dc-SQUID (0.27 eV).
In this research, we considered the degradation of the energy resolution which is caused by the high-frequency cutoff. There are two main factors that limit the frequency band. The first one is a loss of waveform information due to a low sampling frequency compared with the inverse of time constant of the optical TES. The second one is a bandwidth of the resonator. We simulated the effect of the first one on the energy resolution. The sum of the intrinsic energy resolution (0.27 eV), readout noise (0.07 eV) and the simulated result (0.25 eV) was 0.37 eV. This is consistent with the experimental energy resolution. We will discuss the requirement of frequency band of MW-Mux to improve the energy resolution.

References
[1] Niwa et al. Scientific Reports 7 (2017) 45660.
[2] J. A. B. Mates et al., Appl. Phys. Lett. 92, 023514 (2008).

Acknowledgment
This work was supported by JST-CREST Grant Number JPMJCR17N4, Japan. MW-Mux chips were fabricated in CRAVITY (Cleanroom for analogue digital superconductivity) in AIST.

• 130
MMC critical temperature switch development with an integrated heater

We developed metal magnetic calorimeters (MMCs) having a critical temperature switch to inject a persistent current on the integrated planar Nb coil. A part of the Nb superconducting loop was fabricated with an alloy of 38% Nb and 62% Ta concentration. The NbTa switch showed a clear superconducting transition at 5.29 K. Persistent currents as large as 120 mA were successfully charged with the critical temperature switch. In addition, we fabricate a meander-patterned metal film on the MMC device. With the on-chip heater operation, only the MMC device can be heated to reach the temperature of the device at the Tc of the switch while keeping the system temperature unchanged. Moreover, a periodic supply of small current pulses on the heater can be used as a reference of gain stabilization signals. We report on the recent progress on this hybrid configuration with multi-channel application of the critical temperature switch.

Speaker: sora kim
• 131
MOCCA: A 4k-pixel molecule camera for the position and energy resolving detection of neutral molecule fragments at the Cryogenic Storage Ring CSR

The MOCCA detector is a high-resolution, large-area molecule camera based on metallic magnetic calorimeters and read out with SQUIDs. Its array of 64 × 64 quadratic pixels with a side length of 700µm covers a total detection area of over 4.5cm × 4.5cm with a filling factor of 99.5%. It will be deployed at the Cryogenic Storage Ring CSR at the Max Planck Institute for Nuclear Physics in Heidelberg, a storage ring built to prepare and store molecular ions in their rotational and vibrational ground states, enabling studies on electron-ion interactions. To reconstruct the reaction kinematics, MOCCA is able to measure the energy and position of multiple incident particles hitting the detector simultaneously.
We present the readout principles used to read out the complete detector using only 32 two-stage SQUIDs, the fabrication of the free-hanging 700µm × 700 µm absorbers and the thermalization using Through-wafer Vias.
We will show latest measurements with a full-scale MOCCA detector at 10 mK using a 6 keV photon source, exhibiting an energy resolution of less than 200 eV, and the very low cross-talk between columns and rows of the detector.

Speaker: Mr Dennis Schulz (Heidelberg University)
• 132
Multilayer Etched Antireflective Structures for Silicon Vacuum Windows

Future instruments employing cryogenic detectors for millimeter and submillimeter astronomy applications can benefit greatly from silicon vacuum windows with broadband antireflection treatment. Silicon is an ideal optical material at these wavelengths due to numerous attractive properties, including low loss, high refractive index, and high strength. However, its high index ($n=3.4$) necessitates antireflection (AR) treatment, which has proven a major challenge, especially for the multilayer treatments required for wide spectral bandwidths. We address this challenge by developing a wide-bandwidth integral AR structure for silicon vacuum windows using a novel fabrication technique, tuning the effective refractive index of each AR layer using deep reactive ion etching (DRIE) and using wafer bonding to assemble the structure.
We present the progress we have made in designing and fabricating such vacuum windows from 100 mm-diameter silicon wafers. We have previously demonstrated a 2-layer AR structure for windows over a 1.6:1 bandwidth and are currently fabricating a 4-layer coating designed for a 4:1 bandwidth. We have also converged on a design for a 6-layer structure optimized to give -20 dB reflection between 80 and 420 GHz (5.25:1 bandwidth), which will be useful for future multicolor Sunyaev-Zel'dovich (SZ) observations.

Speaker: Theodore Macioce (California Institute of Technology)
• 133
Nanoscale Phononic Crystal Membranes for Low Temperature Detector Applications

Nanoscale phononic crystals (PnC) are promising components for several low temperature detector technologies, such as bolometers, transition edge sensors and kinetic inductance detectors (KID). Recent experimental and theoretical studies demonstrate a wide range of tunability for thermal properties of PnCs with correctly chosen geometry. [1-2] Low temperature applications of PnCs often rely on modifications in the phonon band structure, which affects DOS and velocity of heat carrying phonons. For instance, reducing thermal conductance and improving heat capacity is important in optimizing responsivity of bolometric detectors. Furthermore, a PnC can be designed to operate as high frequency notch filter matched to the energy gap of a superconductor. This can effect can improve sensitivity of KIDs by restricting escape of quasiparticle recombination phonons from the KID inductor. [3]

In this work, we discuss theoretical design process of thin film PnCs for low temperature detector applications. We develop a 3D finite element simulation model based on scattering of elastic waves from the PnC, and use it to estimate phonon escape probabilities. Our calculations demonstrate that obtaining a full band gap for Hafnium at ~32 GHz is possible with simple PnC designs that are producible with current nanofabrication techniques. PnC filters can attain extremely high reflection for the recombination phonons, and effectively no restriction for the low frequency thermal phonons, thus preventing excessive heating of the KID inductor. We also demonstrate that a full band gap is in fact not compulsory, and positive effects can be obtained with less extensive modifications to the phonon spectrum.

References:
[1] N. Zen, et al. Nat. Commun. 5, 3435 (2014).
[2] T. A. Puurtinen and I. J. Maasilta, AIP Adv. 6, 121902 (2016).
[3] K. Rostem, P. J. de Visser and E. J. Wollack, Phys. Rev. B 98, 014522 (2018).

Speaker: Dr Tuomas Puurtinen (University of Jyväskylä)
• 134
Near Infrared and visible TiN- based parallel-plate capacitor kinetic inductance detectors

We report on the development of near-IR and optical parallel plate capacitor lumped-element kinetic inductance detectors (LEKIDs) for astronomical applications. The parallel-plate capacitor is made of a TiN base electrode, Al2O3 dielectric and Nb upper electrode. For a given frequency readout bandwidth, compared to the interdigitated capacitor geometry, the use of the parallel-plate capacitor allows us to significantly reduce the size of optical LEKIDs resonating at low frequencies (1-1.3 GHz) [1].The resonators which were successfully frequency multiplexed thanks to the change of the upper electrode area, exhibit internal Q-factors up to 3 × 10^6 at 72 mK. The array was illuminated using a white light and 890 nm monochromatic near infrared LEDs. In this paper, we will present the design, fabrication and experimental results.

[1] Beldi, S., Boussaha, F., Chaumont, C. et al. J Low Temp Phys (2018) 193: 184. https://doi.org/10.1007/s10909-018-2035-8.

Speaker: Samir BELDI (GEPI, Observatoire de Paris, PSL Université, CNRS, 75014 Paris – France)
• 135
New Approaches to Very Low-energyCalibration of Cryogenic Detectors

The search for dark matter candidates using solid crystals operated at cryogenic temperatures, push towards a lower energy threshold at each development stages for the detectors. Consequently, new approaches for detector calibration at the proposed energy scales are necessary. In the case of SuperCDMS SNOLAB, energy thresholds in the range of few eVs are expected. In this talk, we are presenting new approaches for the calibration of cryogenic detectors in eV energy range, using LEDs of various wavelengths operated at cryogenic temperatures. In addition, we will present the design of a low-energy electron source for calibration in the same energy range.

• 136
NEXUS@FNAL

The Northwestern EXperimental Underground Site at Fermilab (NEXUS@FNAL) is an underground cryogenic facility that has 300 meter water equivalent shielding. A dilution refrigerator operating at 10 mK, a DD generator producing 2.5 MeV neutrons, and a suite of optical and X-ray calibration sources are being deployed at the facility. The expected background level at NEXUS is 100 events/keV/kg/day. We present the status of the NEXUS facility and the near future plan for operating SuperCDMS R&D detectors for dark matter searches and calibrations in this facility.

Speaker: Ziqing Hong (Northwestern University)
• 137
Noise reduction techniques for the CUORE experiment

CUORE is a ton-scale underground array of $988$ $\mathrm{TeO}_2$ crystals operated as bolometers at about $10 \: \mathrm{mK}$ in the INFN Gran Sasso National Laboratories (LNGS). Its main scientific goal is searching for $0\nu\beta\beta$ decay of $^{130}\mathrm{Te}$. Each crystal is equipped with an NTD thermistor whose voltage is low-pass filtered, amplified and continuously digitized at a sampling frequency of $1 \: \mathrm{kHz}$. The standard data processing is based on building and applying an optimum filter on waveforms extracted with time windows of 10 s. The conflicting requirements of reducing the pile-up and enhancing the discrete Fourier Transform resolution forbid a significant enlargement of the time window. Both coherent and non-coherent noise components at low frequency were identified. A complete removal of such noise components would yield a resolution improvement of $\sim 18\%$. The most recent noise reduction techniques, including the implementation of an Infinite Impulse Response notch filter will be presented.

Speaker: Mr Guido Fantini (GSSI / INFN)
• 138
ON-CHIP POLARIMETRY FOR THE SPICA B-BOP INSTRUMENT

SPICA is one of the three projects competing for the ESA M5 mission. The three SPICA instruments share the focal plane of a 2.5 m diameter telescope cooled to 8 K, to achieve ultimate sensitivity measurements in the Far-IR and submm domains. The B-BOP camera, one of these instruments with unprecedented polarimetric capabilities, is mainly devoted to reveal the role of magnetic field in many astrophysical processes.
For this space application, a simple, robust, easy to assemble facility needs the integration of the instrumental polarimetric function at the heart of the detectors. The innovative side of these detector chips is the development of submillimeter bolometers adapted to measure the linear polarization and suited to retrieve the I, Q, U Stokes parameters without any mechanism. In parallel, the other goal is to produce detectors with two orders of magnitude better sensitivity than the Herschel Observatory, using doped silicon meanders (“Only leg detectors”) cooled to 50 mK. We describe the different functions of the instrument built around an optical path aimed to minimize the induced self-polarization.

Speaker: Dr Louis Rodriguez (AIM/DAp/IRFU/DRF/Commissariat à l'énergie atomique et aux énergies alternatives)
• 139
Optical and Tunneling Studies of Energy Gap in Superconducting Niobium Nitride Films

We have prepared superconducting niobium nitride (NbN) films and NbN/AlN/NbN tunnel junctions to investigate the energy gaps by measuring the optical conductivity with time-domain terahertz spectroscopy and by tunneling spectroscopy, respectively. A 41-nm-thick NbN film was deposited on a 0.3-mm-thick single crystal MgO substrate by reactive dc magnetron sputtering. The critical temperature (Tc) and the dc resistivity at 20 K were 14 K and 69 micro-ohm-cm, respectively. The transmission spectra of the NbN film on the MgO substrate were measured at several temperatures from 6 K to 20 K. The experimental result at 6 K showed that the real part of the conductivity rises from a value near zero at about 1.2 THz (= 4.96 meV = 4.1kTc) which is the gap frequency of the film, where k is the Boltzmann’s constant. With increasing the temperature, however, we found that the superconducting gap became ill-defined due to the broadening of the onset of absorption. This may be attributed to the finite quasi-particle lifetime in the NbN film. On the other hand, from the I-V curve measurement of the high quality NbN/AlN/NbN tunnel junction with the current density of 100 A/cm2 at 2.5-16 K by a dilution refrigerator, we observed large smearing of the gap voltage as the temperature increases. This also indicated the lifetime broadened superconducting density of state. The temperature dependence of the lifetime estimated from both results will be discussed.

Speaker: Prof. Yoshinori Uzawa (National Astronomical Observatory of Japan)
• 140
Optical Characterization of BICEP3 and the Keck Array from 2016 to 2019

The BICEP/Keck experiment (BK) is a series of small-aperture refracting telescopes observing degree-scale Cosmic Microwave Background (CMB) polarization from the South Pole in search of a primordial B-mode signature. This B-mode signal arises from inflationary gravitational waves interacting with the CMB, and has amplitude parametrized by the tensor-to-scalar ratio $r$. Since 2016, BICEP3 and the Keck Array have been observing with 2400 antenna-coupled transition-edge sensor detectors each, with frequency bands spanning 95, 150, 220, and 270 GHz. Here we present the optical performance of these receivers from 2016 to 2019, including far field beams measured in situ with an improved chopped thermal source and instrument spectral response measured with a field-deployable Fourier Transform Spectrometer. As a pair differencing experiment, an important systematic that must be controlled is the differential beam response between the co-located, orthogonally polarized detectors. We show per-detector far field beam maps and the corresponding differential beam mismatch that is used to estimate the temperature-to-polarization leakage in our CMB maps and to give feedback on detector and optics fabrication. The differential beam parameters presented here were estimated using improved low-level beam map analysis techniques, including efficient removal of non-Gaussian noise as well as improved spatial masking. These techniques help minimize systematic uncertainty in the beam analysis, with the goal of constraining the bias on $r$ induced by temperature-to-polarization leakage to be subdominant to the statistical uncertainty. This is essential as we progress to higher detector counts in the next generation of CMB experiments.

Speaker: Tyler St Germaine (Harvard University)
• 141
Overview of SuperCDMS Experiment

The SuperCDMS collaboration has entered the construction phase for the upcoming SuperCDMS SNOLAB experiment. By 2025 we will probe nuclear-recoil dark matter between 300 MeV and 10 GeV and electron recoil dark matter down to 500 keV with world-leading sensitivity. I will review the status and plans for the SuperCDMS SNOLAB experiment, and discuss recent science results from surface dark matter runs in the electron-recoil plane.

Speaker: Dr Ziqing Hong (Northwestern University)
• 142
Performance of a low-parasitic frequency domain multiplexing architecture

Frequency division multiplexing (FDM) is a readout technique for transition edge sensor-based bolometer arrays used on telescopes including SPT-3G, POLARBEAR-2, and LiteBIRD. Here we present the latest progress and plans for development of a minimal-parasitic FDM architecture. This technology will enable ultra-large focal planes for future instruments such as CMB-S4. Reduced wiring length between the MHz resonators and series SQUID array ameliorates parasitic impedances which contribute to crosstalk and limit operation of low-resistance bolometers. We have demonstrated improved electrical performance including reduced stray inductance and reduced stray resistance. This will enable operation of low-resistance bolometers and higher multiplexing factors in future arrays. Operating bolometers at lower resistance will decrease the contribution of readout noise to the total NEP by decreasing the required voltage bias. Ongoing work seeks further improvement in circuit parasitics and a laboratory demonstration of this architecture integrated with low-resistance bolometers.

Speaker: Dr Amy E. Lowitz (Kavli Institute for Cosmological Physics - University of Chicago)
• 143
Planar Self-Similar Antennas for Broadband Millimeter-Wave Measurements

From extremely broadband functionality to easily scalable designs, self-similar antennas offer a strong set of benefits. With a four-arm layout, self-similar designs also become geometrically suited for dual-polarization through excitations of opposing arms. However, there has only been limited use of these devices for millimeter-wave detectors. One field for such antennas is the Cosmic Microwave Background (CMB), which encompasses a wide frequency range and is now actively focusing more on polarization measurements.

We look at multiple planar self-similar antenna designs with simulations in HFSS (High Frequency Structure Simulator) and ongoing physical testing. They all exhibit broadband operation between 130-230 GHz and can couple to both linear polarizations through the previously mentioned four-arm symmetry. Simulations include each antenna design coupled to an extended, AR-coated lenslet. From these, a basic bowtie-like arm design produced high polarization efficiency and small frequency variation with moderate efficiency, while a hybrid trapezoidal design provides high efficiency with small polarization fluctuations. Current fabricated versions of each are being tested, coupled to multichroic Kinetic Inductance Detectors (mKIDs). These planar self similar antennas, when implemented in CMB and other detectors, could improve observations while simultaneously simplifying fabrication and detector layout designs.

Speaker: Jeremy Meinke (Arizona State University)
• 144
Precision measurement of the absorbed dose in heavy ion beam by superconducting transition edge sensor

Calorimetry of the absorbed energy in heavy ion is very effective for minimizing of the uncertainty in dose rate measurement. Therefore we have been developing the precision heavy charged particle detector applying the superconducting transition edge sensor (TES) coupled to a tin absorber. In LTD 17, we reported our first experimental result, in which we succeeded to detect the helium ions at the HIMAC (Heavy Ion Medical Accelerator in Chiba) in National Institute of Radiological Sciences. However, the signal property were significantly degraded by the noise events which derived from the incident on neighboring region of the detection area or the event through the absorber. Thus, in order to reduce these noise events, we have greatly improved the experimental setup on the beam line. First a 1mmφ Ta collimator is introduced so that the heavy ion beam will only hit the absorber. Further, we changed the angle of the TES against the ion beam, so that the heavy ion beam which went through the absorber will never hit the superconducting bilayer. As a result, the noise during the experiment was reduced dramatically, enabling us to collect high quality data of heavy ions measured by TES.

Speaker: Dr Masashi Ohno (The University of Tokyo)
• 145
Precision Measurements of Beta Spectra using Metallic Magnetic Calorimeters within the European Metrology Research Project MetroBeta

MetroBeta is a European metrology research project aiming at the improvement of the knowledge of the shapes of beta spectra, both in terms of theoretical calculation and measurement. The most prominent experimental work package deals with the measurement of the spectrum shapes of several beta emitters by means of metallic magnetic calorimeters (MMCs) with the beta emitter embedded in the absorber. This approach has in the past proven to be among the best beta spectrometry techniques, in particular for low energy beta transitions.
New MMC chips have been designed and optimized for five different absorber heat capacities, enabling the measurement of beta spectra with Q values ranging from few tens of keV up to ~ 1 MeV. Four beta spectra have been measured with high energy resolution and statistics up to 10E7 counts within the project, three from pure beta emitters (C-14, Q = 156.5 keV; Tc-99, Q = 293.8 keV; Cl-36, Q = 709.5 keV) and one having a small decay branch to an excited level at 21.5 keV of its daughter (Sm-151, Q = 76.3 keV).
This contribution focuses mainly on the measurement of Cl-36. Whereas for the lower energy spectra of Sm-151, C-14 and Tc-99 simple gold or silver absorbers can be used, spectra with Q values higher than ~ 500 keV will be distorted by the escape of bremsstrahlung from the absorber. This is the case of Cl-36. Monte Carlo simulations indicate that composite absorbers with the beta emitter embedded in a low atomic number material (Cu) and an outer layer of high atomic number (Au) can minimize this source of spectrum distortion.
The spectrum of Cl-36 measured using both gold and composite copper-gold absorbers will be presented and compared with the corresponding Monte Carlo simulations. The spectra of the other nuclides will also be shown.

Speaker: Mr Martin Loidl (CEA Saclay)
• 146
Process development for dual-thickness, multi-absorber x-ray microcalorimeter arrays

We are developing new focal plane arrangements of x-ray microcalorimeters to meet the needs of future instruments for x-ray astrophysics. The prototype focal plane for Lynx, a mission concept for an x-ray telescope, requires the flexibility to image large areas with moderate resolution across the 6 keV x-ray band while also imaging point sources with very high resolution for soft x-rays. Integration of multiple types of microcalorimeter into the same focal plane can lead to fabrication challenges. We tackle the large area array through a combination of 25 and 50 micron absorber pixels grouped with twenty-five thermal links to one TES (the Hydra design) and use a demonstrated high energy resolution detector design with a relatively small TES and an absorber thickness of 4 microns of Au. We use thermal links with micron-scale widths to keep the heat capacity of the thermal distribution network a relatively small fraction of that of the device. The narrow wires of Ti/Au are tuned to a target resistance of 20 mOhm/sq. We evaluate the width dependent resistance of the wires and their tendency to anneal to determine what impact those effects will have on the ultimate design. To address the array with ultrahigh resolution capability, we reduce the thickness of the absorber to as low as one micron. We show a substitution of photoresist with an AlOx hardmask enables fine gaps between these absorbers as narrow as 1 micron. Integration of this hardmask with a conventional photoresist mask enables ion mill definition of 4 micron and 1 micron absorbers in the same focal plane. We describe the fabrication methods and materials characterization for the devices. Progress toward a completed Lynx prototype is presented.

Speaker: Dr James Chervenak (NASA GSFC)
• 147
Properties of the SQUID readout chain under development for the ATHENA X-IFU instrument

Superconducting Quantum Interference Devices (SQUIDs) are used as the standard first-stage amplifier for the readout of cryogenic TES-based detector arrays, and multiplexing techniques are used to minimise the heat loads and complexity of TES readout systems. Frequency domain multiplexing is the baseline for the readout of an imaging array of TES-based microcalorimeters the X-IFU instrument on the future ESA Athena X-ray telescope.